A big Carnival cruise line sits in the background and we see Dave fumbling with paperwork and passports. The Chipmunks (Simon and Theodore) and the Chipettes (Brittany, Jeanette and Eleanor) are dancing together as Dave tries to do a headcount. He quickly realizes there’s no … “ALVIN!!!” Alvin comes sliding down the mooring lines and tells Dave he already checked out their room and reserved the bed closest to the window for himself, signed them up for parasailing and ordered some virgin Pina Coladas. The Chipmunks/Chipettes are upset that Alvin staked claim on the bed and suggested to Dave that he create some rules. Alvin is annoyed stating this was supposed to be a fun family vacation.
Aboard the ship, we quickly see the Chipmunks and Chipettes start getting into trouble by spraying tanning lotion all over the deck and skating across the slippery surface. Dave slips as well, sending his umbrella drinks everywhere. Alvin is later seen in the ship’s control room talking on the intercom saying that all kids are allowed access to the adult-only serenity deck. Kids flood the deck and spray down the adults with squirt guns. A leering look from the Captain and Alvin quickly relinquishes the intercom mike.
That night in their cabin, Dave tells the Chipmunks that he is going to dinner with the captain to try and smooth over Alvin’s mess. Simon helps Dave tie his bow-tie in the bathroom and tells Dave that Alvin is like a racehorse. The tighter you hold the reigns, the more the racehorse will buck. If Dave would just let lose Alvin’s reigns a little bit, Alvin could possibly prove that he is capable of rising to the occasion. Dave agrees with Simon’s advice and tells the Chipmunks/Chipettes that he ordered room service and to keep themselves entertained they can order a movie of their choice stating they are old enough to make their own decisions. Theodore stops Dave before he leaves and gives him a macaroni necklace he made for him.
Dave is at the captain’s table getting a ripping from the Captain about the Chipmunk’s behavior problems. Dave tries to laugh it off when the “Pelican” (the cruise ship’s mascot) pours a dish of hot gravy all down Dave’s leg. As Dave is leaving, he runs into the Pelican again and asks what his problem is. The Pelican tells him that he should know and removes his head to show that he is “Uncle” Ian. Ian explains that after caging the Chipmunks and Chipettes and passing on Beiber … twice, no one in the music industry would hire him. So he has a job on the cruise ship as its mascot. He warns Dave that he will tell the Captain and have them booted from the boat if Alvin creates any more mischief.
While this is going on, Alvin removes his PJs to show he is wearing a James Bond-esque suit (equipped with James Bond puns) and is about to head to the casino. Simon reminds him of Dave’s wishes to which Alvin quickly repeats that Dave said they are old enough to make their own decision. Simon tells him that it meant movie choices. Alvin changes the movie from Theodore’s choice of rated G lollipop action to Jungle Monsters 4, and leaves. Simon quickly rushes off to stop Alvin. The Chipettes want to go Salsa dancing, but have nothing fun to wear, so Eleanor fashions them some outfits out of a gift basket wrapper and they go off to the club.
Jeanette, shaking her tail, accidentally steps on the shoe of a mean girl and quickly apologizes. The mean girl doesn’t take it very well and challenges the Chipettes to a dance-off against her and two friends. The Chipettes win the dance off, and we see Alvin in the casino hitting on a lady who just won at Craps. Simon in a mad rush to find Alvin and return him to the room uses a slot machine lever to jump onto a drink tray, thus causing the machine to hit the jackpot.
Theodore back in the room is terrified of Jungle Monsters 4 when Dave returns and asks where everyone is. Dave leaves to find the others and turns off the light leaving Theodore alone in the dark. Simon finds Alvin talking with the Craps winning lady about the same time Dave does. He tries to run interference saying “they are not gambling” when a casino attendant presents Simon with his Jackpot winnings. Dave is mad at everyone back in the room and threatens they will not perform at the International Music Awards show (their ultimate destination, although it’s not clearly stated).
The next day, as punishment, Dave has got the captain to agree to some entertainment for the Chipmunks/Chipettes … shuffle boarding. As they are playing, Dave quickly falls asleep in the lounge chair. Alvin gets an idea to trade the donuts Theodore is eating for a bigger kid’s kite. Alvin had been bugging Dave to go hang-gliding since they’d arrived. Alvin is having a great time up on the kite with the Chipettes and Theodore holding the line. Simon said he’s not going to help Alvin out of another one of his misadventures. Soon the kite gets to be too much for everyone and Simon ties it to Dave’s lounge chair. The kite quickly becomes too much for the lounge chair, dragging a snoring Dave across the ship until they are unraveled and flying out into the open sea. Dave wakes up in time to see the kite fly off with his kids and quickly commandeers the hang-glider to go after them. As he is buckling himself in, Ian/Pelican sees him and says he has to register at guest services first. They both get whisked off the boat on the hang-glider, and Ian unbuckles the belt causing both of them to fall into the open ocean … far away from the cruise ship.
The chipmunks make it to an island where Simon starts a beach fire with his glasses utilizing the sun. On the other side of the island, Dave and Ian are swimming to shore. Later that night Theodore blows out the campfire because Dave always turns out the lights after saying good night. The next morning, the Chipmunks/Chipettes go out in search of food. They find a lone mango when they hear a rustle in the leaves. Alvin launches the mango and it his Zoe, an alleged former UPS pilot who crash landed in the ocean 8-9 years ago. She tells the Chipmunks that she’s not alone and takes them back to her tree house to meet her friends: Spaulding, Calloway, Nerf, and some others … basically, every manufacturer of a ball (a la “Castaway”). They think she’s a little loony, but enjoy her company. Zoe helps them out with food and first aid when Eleanor sprains her ankle. Britney complains about her appearance and odor, while Simon is bitten by a jungle spider and quickly hallucinates himself into being “Simone” a French-speaking, adventure-loving enthusiast.
The next few days are filled with Simone becoming Alvin and vice versa, and Jeanette becoming Britney and vice versa. Alvin, figuring he’s no longer the popular one, stakes out to make a shelter. Britney, realizing she’s no longer the pretty one, helps Alvin and builds another shelter for the girls. Mean while, Simone jumps off a waterfall into a pond and rides a ferocious looking fish to just behind the waterfall, into a cave. There, he scurries inside an opening and finds tons of gold. He brings out a gold crown for Jeanette and Zoe immediately requests to know where he found it. Zoe runs back to her tree house and tells the balls that they found the treasure, the treasure she’s been looking for for 10 years.
Meanwhile, Dave and Ian are still going through the forest looking for the kids. Dave has to explain at length to Ian why he considers the Chipmunks and Chipettes his children and eventually comes to the realization that maybe the Chipmunks/Chipettes didn’t make it to the island. Ian at one point changes his attitude about Dave ruining his life and tells him that he’s a good father. While hugging it out Ian quickly tries to eat Dave’s macaroni necklace that Theodore made him. A scuffle ensures, one in which Theodore sees and mistakes it to be the Jungle Monster (from Jungle Monsters 4) because Ian is still in his Pelican suit. Theodore can’t look away. The necklace gets tossed far from the scuffle and ends up hitting Simone. Theodore rushes to Simone as he pretends to be “nearing the light” and says to tell Jeanette he will watch over her with angel wings. Theodore realizes the Simone was hit with Dave’s necklace. We next see Dave and Ian wrestling on the ground with Ian getting the advantage. Dave looks up and sees Theodore holding his necklace. They all embrace.
Back at the shelters, Brittany and Alvin at trying to come to terms with the fact Dave isn’t looking for them because Alvin has been such a pain in the butt for years, it’s no wonder he doesn’t want to find the Chipmunks and Chipettes. So Alvin and Brittany start dolling out orders to make a raft. As he finishes, Dave strolls up and says “how can I help?” The girls embrace Dave, and Alvin turns his back. Alvin tells Dave he didn’t think he was coming because Alvin had been such a pain for all those years. Dave tells him that he is a pain, but he’d come no matter what. They hug, and Dave tells Alvin that he is in charge of the raft. As they are building a raft, Jeanette and Simone are looking for food when “Callaway” hits Simone on the head. Jeanette is quickly forced into a hole by “Spaulding.” With the raft almost ready, Dave and Alvin go looking for Jeannette and Simone. They find Simone, who has been knocked back into Simon (and updated that he is “dating” Jeanette), but they can’t find Jeannette.
Zoe captures Jeanette and ties her up to make a rappelling line for her to go into the cave and retrieve as much gold as she can. Immediately the ground starts to shake, and they realize the island they are on has an active volcano. Zoe yells at Jeanette to stuff her chipmunk cheeks with the gold and hoists her out. Dave and some Chipmunks show up to rescue Jeanette. They almost have her to safety when Zoe steps on her rappelling line over a ravine. Simon swings to the rescue, freeing Jeanette and the Chipmunks flee to safety. The volcano continues its eruption and Dave is knocked off the log connecting both sides of the ravine and is barely hanging on by a branch. Alvin quickly rushes to the rescue with Ian telling Dave he has him, he’s his dad, he’s going to rescue him, and for Ian and Zoe to help. Zoe is raving about how everyone thought she was mad, but she knew there was treasure and thanks to Dave … he ruined her life. Ian tells her that it’s easy to let revenge and hatred take over, but she should just let it go and help Dave up. But if she doesn’t, Ian can inherit the Chipmunks and make millions, so he’s good either way.
Lava bombs have started to erupt from the volcano, and the raft is waiting on the shoreline. Ian, Alvin, Dave and Zoe come running from the jungle, hop on the raft and start paddling away from the island. Out to sea, Zoe apologizes to Jeanette for going crazy, and Jeanette gives her the crown that Simone gave her as proof the treasure existed. A coast guard helicopter is flying overhead and locates the raft.
We then see the Chipettes and the Chipmunks performing at the International Music Awards. Ian tells Dave it’s good to be back and that he sold Zoe’s story to the movie industry. The movie ends with Dave, Chipmunks and Chipettes on a flight home when we hear Alvin over the intercom saying Thank you for flying Air Alvin to Timbuktu. If you are not going to Timbuktu, please press your overhead light to alert the flight attendant. Immediately all the lights are turned on and Dave shouts “ALVIN!!!” Credits.
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