NOTE: This spoiler was submitted by Kevin D
"Dark Shadows" opens in Liverpool, England in 1760 with a sweeping shot of tall mast ships at dock that highlights the ornate carving of a mermaid on one particular ship's bow. The Collins family of wealthy fishing industry magnates is departing the Old World for a new life in Maine to expand the family empire. We're introduced to the young child Barnabas Collins as his father ushers him onto the ship...and we meet Angelique Bouchard, a young servant girl who works for the Collins family.
In Maine, the Collins family prospers, establishing the small town of Collinsport that's centered around their fishing interests. Soon, the family puts down permanent roots in America by designing and building the most elaborate mansion built in the colonies: a massive 200-room palace called Collinswood that's riddled with secret passages and intricate marble carvings most often depicting seahorses, dolphins, mermaids/mermen, and other mythical sea creatures. Massive oil paintings of Collins family members line the hallways and a ridiculously large chandelier holds court in the center of the great room that bleeds into the staircase to the upper wings.
Angelique has grown into a vixen who loves and covets Barnabas -- but he doesn't return her affection, despite occasionally using her body for gratification. Angelique is scorned and turns to dark magic to enact her revenge, starting with bewitching a small seahorse sculpture and smashing it...which causes one of the chateau's massive seahorse statues to plummet from the roof and crush Barbabas' parents while they were strolling the grounds. Barnabas grieves for his parents and assumes the mantle of family patriarch and master of the Collins fishing and canning empire. He falls in love with a young woman named Josette, whom Angelique becomes excruciatingly jealous of. Angelique bewitches Josette and causes her to walk off "Widow's Cliff"...a precipice near Collinswood Manor where many young woman have killed themselves with broken hearts.
Barnabas races to save Josette but is too late...under the spell, she leaps to her death. He follows her, but when he crashes into the black rocks below, he does not die. Instead, his skin turns alabastar and his nails grow to monstrous length and sharpen into claws. His eyes bleed tears of blood. He's a vampire now.
This was Angelique's curse: to take away the woman he loved, and then curse him to live forever so that he would always miss her.
Barnabas then tries to learn dark magic himself because he's obsessed with defeating Angelique before she's able to destroy the Collins family as she's vowed. Barnabas' father had always said that family was more important than any riches in the world and without his love Josette Barnabas now pledges to be his family's protector forever, putting his immortality to a purpose.
In his studies of the occult, Barnabas learns the Devil's real name, Methestopheles, and sees his emblem as an "M" marking his domain on the Earth. But he does not learn any magic that can defeat Angelique, who has powered up and waged full war on Barnabas by turning the villagers against him. They storm Collinswood Manor like that scene in Frankenstein where they bring the torches to kill the monster...but these townsfolk grab Barnabas, lock him in a coffin, and chain it shut so that he will be forced to live forever underground with no one to talk to and no hope of escape.
While he's imprisoned in the ground, Angelique mounts a considered campaign to eclipse the Collins family and make Collinsport her own...hoping to take over the entire town and turn it into "Angel Bay". Angelique is immortal too, though the price for her immortality is that she's essentially a living mannequin -- her skin is like porcelain, but if she gets hit with something, it cracks and inside it's shown that there's no blood, flesh, or bones...just emptiness. Every generation, Angelique revamps herself into a "descendent" of herself, taking on the identity of a granddaughter who inherits the business she's built...which is a fishing empire to rival the Collins'.
In 1972, Angelique has assumed the identity of "Angie Bouchard", her 6th incarnation (after her original one in the 1760s and ones in the 1800s, 1850s, 1890s, 1920s, and the 1970s).
Barnabas is reawakened when a construction crew building a McDonalds unearths his coffin. They make the mistake of opening it, and Barnabas quickly kills and drinks the blood of the entire work crew. Looking up, Barnabas sees the Golden Arches "M" of McDonalds and is scared, thinking it is the "M" of the Devil's name. He then interprets pretty much everything about life in the 1970s as satanic magic -- such as cars, television, radio, and electricity.
This portion of the movie becomes a fish out of water story as Barnabas adjusts to live in the 1970s -- the time period during which the Dark Shadows TV show aired. The film evokes the soap opera fell of the original series, with multiple layers of plot that feel like a condensed season or three of the TV show.
In short order, Barnabas makes it back to Collinswood Manor and finds it in a state of disrepair because Angelique has driven his family into bankruptcy: all that is left of the Collins empire is a handful of small fishing boats. The family lost their cannery long ago and have resorted to selling off whatever valuables they can scrounge to stay alive. Most of the 200 rooms in the manor have been sealed shut to save money, and the family eats scraps and tough, unappetizing cuts of meat for dinner using steel utensils that were made to resemble the fine silver they hocked long ago.
Barnabas hypnotizes the house's caretaker Willie Loomis (Jackie Earl Haley) and orders him to clean Barnabas up (as he's still wearing ancient clothes caked in dirt and blood) and then introduce him to the last 4 remaining Collins family members: Elizabeth Collins Stoddard (Michelle Pfeiffer) and her daughter Carolyn (Chloe Grace Moretz) and Roger Collins (Jonny Lee Miller) and his son David Collins (Gulliver McGrath). No mention is made of whatever happened to Elizabeth's husband, but Roger's wife (and David's mother) drowned a few years ago due to one of Angelique's plots to bring misery to the family. David's mother still comes to him as a ghost, though no one else can see her --- and this has caused everyone to believe David is insane, so the family brought Dr. Julia Hoffman (Helena Bonham Carter) into the mansion to care for his mental health.
We learn later in the film that Carolyn's been hiding a secret: another plot of Angelique's to make the Collins family miserable happened when Carolyn was a baby and Angelique conjured a werewolf to nip the baby in the crib, hoping that when she'd reach puberty she'd wolf out and bring torment to the family. These gothic flourishes and brushes with the supernatural explain why Carolyn and David have no problem accepting Barnabas into the household, despite him clearly being the same being that was depicted in the giant painting of their ancestor Barnabas that hangs over the fireplace in the Great Room.
Elizabeth thinks Barnabas is a nut dressed up in a costume come to extort the family for money. Barnabas proves who he really is by using his elegant cane (with a metal wolf's head handle) to open an elaborate secret passageway that was concealed in a fireplace in the study. Though Elizabeth was aware of some of the secret doors and cubbies hidden in the house, she didn't know the fireplace could come alive with a clockwork mechanism that made the bronze wolves adorning it howl and push the fire pit back to reveal a secret tunnel leading to a treasure cave where famous paintings and ornate jewelry was stashed.
Barnabas repeats his father's words to her that family is more valuable than riches and Elizabeth laments that all the time they were living in squalor they had all these riches sitting in this secret room and never knew it.
Using this wealth, Barnabas sets about restoring the mansion and rebuilding the Collins family's business empire -- all the while adjusting comically to the 1970s and how much the world is changed.
A young woman calling herself Victoria Winters arrives at the mansion to fill the position of governess for David Collins...but in reality she's the reincarnation of Josette. We learn later that since she was a baby, Josette's ghost has been haunting her. Originally she was named Maggie Evans...but her family couldn't deal with her constantly talking to "herself" when they'd catch her having conversations with Josette's ghost so they sent her to live in a mental institution, where she was trapped until recently when she escaped. The ghost of Josette told her to come to Maine and apply to be the governess. She renamed herself "Victoria Winters" because on the train rid to Maine she saw a poster advertising WINTER skiing in VICTORIA, British Columbia. She then hitchhiked with a bunch of stoner hippies in a van to make it to Collinswood Manor and interview with Elizabeth for the job.
There's a fun bit when Victoria first meets David where he appears wearing a sheet trying to scare her by pretending to be a ghost at a family dinner...and then not long after we see a figure wearing that sheet watching Victoria up in her room and when she pulls off the sheet it's Josett's ghost. Of course, Victoria is not scared of ghosts because she's seen them her entire life.
The film builds romantic tension between Barnabas and Victoria as he is attracted to her because she is the modern embodiment of Josette, though he cannot see her ghost and doesn't realize that Josette has been maneuvering things so that Victoria ultimately becomes Josette reborn in 1972.
Meanwhile, Angelique realizes Barnabas has returned and renews her war with him and the Collins family. She comes to the manor to taunt Barnabas, but is still wildly sexually attracted to him. Barnabas shuns her again, and she renews her vow to destroy his family completely.
Barnabas uses his hypnotic powers to steal Angelique's fishing contracts from her -- including one owned by a captain played by Christopher Lee in a cameo. Angelique is obsessed with her "Angie" persona and being the most beloved person in town, so she decides to make Barnabas the most hated man in town and do again to him what she did in 1760 by getting him locked up into a coffin for another few centuries.
Barnabas rebuilt the Collins Cannery Company and Angelique eventually tries to buy it from him for $1.75 million (around $10 million in 2012 dollars); he turns her down and then in a burst of anger at his refusal to sell the two of them have what can only be described as monster sex, since the two immortals smack each other around, claw the furniture, fly around from ceiling to floor and back, and wreck the room doing it. This happens in Angelique's office, which has portraits of her from every incarnation of her long life...and also contains the mermaid figurehead from the ship that brought the Collins family (and Angelique) to the New World 200 years or so before.
Barnabas says he will never love Angelique and she hatches a plot to destroy his family once and for all -- she just needs the right excuse to set the townspeople against Barnabas.
That excuse comes when Barnabas kills Dr. Hoffman when he catches her using blood she'd taken from him to try to turn herself into a vampire to become young and beautiful forever. Dr. Hoffman had lied to Barnabas and said she was trying to find a way to turn Barnabas into a man again -- since the logic was that if a man was turned into a monster, he should be able to be turned back from monster to man. As he drank her blood and drained her, Dr. Hoffman grew fangs and turned into a vampire before passing out. Barnabas thinks she's dead, so he and Willie shackle her to a large cement block and throw her in the ocean (where she'll eventually wake up and open her eyes underwater, implying she'd be the villain out for revenge in a sequel if one is made).
Barnabas throws a big party featuring Alice Cooper as a guest to show the town that the Collins family is rich and powerful again. There's a running joke where Barnabas mistakes "Alice" for a woman -- and the singer plays himself in the movie. Barnabas catches Roger Collins having sex with a coatcheck girl and decides to give him some money and send him away since he clearly doesn't care about David.
After the party, David is almost killed when Willie accidentally drops a giant disco ball as he was taking down the decorations from the Alice Cooper concert. Barnabas saves him, but in doing so he reveals he was a vampire because he moved too quickly for a human and when he stopped moving he was standing in sunlight -- which makes him catch fire.
No one is particularly surprised by the news that Barnabas is a vampire.
Meanwhile, Angelique decides to use the disappearance of Dr. Hoffman to set the town against Barnabas. First, she uses magic to rupture the gas lines and burn down the Collins cannery. Then she lies to the townspeople and says that Barnabas hid the bodies of lots of people he murdered inside there to incinerate them. The townspeople are either very stupid or she's using magic on them because they form a mob and march to Collinswood Manor to destroy the Collins family...just like in the 1700s.
Angelique locks Barnabas in chains in a coffin and hides him in his parents' crypt and then claims his disappearance proves he killed all those people and then set the fire at the cannery to burn the whole town to the ground. The stupid villagers believe her until David finds Barnabas in the coffin and unchains him. There's a funny bit where Barnabas thought he was locked away for centuries again or at least decades, but David tells him it was only 20 minutes. Angelique intended it to be centuries however, and as a new torment she pulled off her dirty panties and stuffed them into Barnabas' face before sealing the coffin so he'd have to smell her scent for hundreds of years (or 20 minutes, whichever came first evidently).
A big fight between Angelique and Barnabas breaks out in the mansion, with Angelique revealing herself to be an immortal porcelain-doll like creature whose skin cracks when struck. Elizabeth Collins has no supernatural powers, but she has a shotgun and starts shooting holes into Angelique like in "Death Becomes Her", but Angelique is just slowed down a little. Then, Angelique makes all the mermaid and monster statues in the house come to life to attack Elizabeth, similar to Professor Magonagal making the statues come to life in the last Harry Potter movie. Angelique also made the paintings come to life to taunt Elizabeth, Harry Potter style. That keeps Elizabeth busy while Angelique battles Barnabas.
Caroln unexpectedly joins the fight as a werewolf and tries to bite Angelique but can only put more holes into her mannequin-like body.
In the end, Carolyn makes the chandelier crash down as a fire Angelique started burns the manor to the ground. David's ghost mother appears as a kind of banshee and her scream pushes Angelique to the floor and knocks the wind out of her, which is just the thing everyone needed to flee the fire and allow Barnabas the chance to mount a successful counterattack on Angelique.
Barnabas corners Angelique and she just sort of gives up. She reaches inside her empty body and pulls out her heart, which is made of pink glass. Barnabas tells her that her curse was that she could never really love anyone. He crushes her heart and her whole body shatters and it's presumably the end of Angelique.
Outside, David asks his mother what they're all going to do now that the mansion has been burned to the ground and Elizabeth says "We will endure", which is the Collins family motto.
Angelique may be dead but she had one last twist for Barnabas. This whole time, Victoria has been under a spell and has been heading to the cliff to kill herself under Angelique's orders. David's ghost mother tells him to tell Barnabas to save her...so Barnabas races to do that.
He's too late, but gets there with more time to spare than the first time when Josette dies because he catches Victoria mid-air and sinks his teeth into her, which somehow gives the ghost of Josette the chance to enter into Victoria's body and cause the transformation into a vampire. So when the two of them land on the rocks, neither die and instead Josette kisses Barnabas inside Victoria's now vampire body. It appears Victoria is now gone and it's vampire Josette who has been reunited with vampire Barnabas and this means Angelique's curse is broken forever because Barnabas will be able to be with his love Josette indefinitely.
The movie ends with one last plunge into the ocean to show Dr. Hoffman is also a vampire, but is still trapped underwater and chained up until someone releases her.