NOTE: This spoiler was submitted by Jeremy

Somewhere in Costa Rica, a team of scientists led by Dr. Michael Morbius (Jared Leto) arrive at a cave. Morbius steps forward to the cave’s entrance and cuts his hand, then holds it out as a swarm of bats begin flying out, drawn to his blood. The rest of the men retreat back to their chopper.

25 years earlier in Greece, we see a young Michael (Charlie Shotwell) living under the care of Dr. Emil Nicholas (Jared Harris), as Michael suffers from a blood disease. The institution they are living in welcomes another child with the same disease, Lucien (Joseph Esson), but Michael refers to him as “Milo” due to the last kid who was there being named that. After some chatting, Milo’s machine starts to falter and he passes out. Michael uses a spring from a ballpoint pen to fix the machine and revive Milo. Nicholas expresses astonishment at this task. Later, Milo is harassed by other kids who taunt him for his condition and kick him while he is down.

Back in the present, Morbius is up for a Nobel Peace Prize in Sweden, but he rejects it and goes on to continue his work. He is treating a young girl, Anna, who suffers from the same condition as him. Morbius works with his girlfriend, Dr. Martine Bancroft (Adria Arjona), who thinks he is pushing himself too hard in his endeavors. It is also said that Milo (now played by Matt Smith) is the benefactor for their project of mixing bat DNA with human blood, as this is what Morbius thinks will cure his disease. He has recovered the bats from the cave for the project. He tests his serum on a lab rat, who appears to die. Moments later, Anna starts to have a seizure, but Morbius is able to take care of her before she suffers a stroke. Martine looks back at the lab and sees that the rat is revived and moving, meaning Morbius’s serum is a success.

Morbius goes to meet with Milo and Nicholas to get more funding to continue his experiments on a ship on international waters. Milo has been living under Nicholas’s care since childhood. Morbius and Milo have become like brothers, but Morbius makes it seem urgent that Milo help him as soon as possible before it’s too late for both of them.

Morbius gathers Martine and other crew members onto a ship for the next stage of his experiment, where Martine will administer the serum to Morbius. After the procedure, Martine is bothered by a surly crew member when they notice that Morbius has broken free from the straps on his chair. They find him crawling on the ceiling, and Morbius attacks the man. Other mercenaries show up, and Morbius, now having turned into a vampiric monster, attacks all of them and drains them of their blood. Martine is knocked unconscious in the struggle, and after Morbius regains his humanity, he watches himself attacking the men on security cameras.

FBI agents Simon Stroud (Tyrese Gibson) and Al Rodriguez (Al Madrigal) are brought on to investigate the crime scene. Martine is found alive, but Morbius has fled after calling in the mayday response. Milo and Nicholas also catch wind of the incident.

Morbius isolates himself in his lab to continue understanding his new condition while also feeding off blood samples to satiate his hunger. He begins to hone his new bat-like powers (flying, super speed and strength, faster reflexes), and the bats in his lab also respond to him as their leader. He is later found by Milo just as he begins to relapse into his monstrous state, but Milo helps him get under control. Realizing that the serum has helped cure Morbius’s disease, Milo wants to get some, but Morbius refuses since he knows the consequences would be dangerous.

Later, Morbius goes to the hospital that Martine is staying at to check on her. A nurse is attacked and killed by a vampire monster, but it’s not Morbius. Just as he hears about this, Stroud and Rodriguez appear to question Morbius, who ends up trying to flee, but he is soon apprehended and taken to a detention center.

Stroud and Rodriguez question Morbius in his cell before he is later visited by Milo. After Milo leaves his cane behind, Morbius realizes that Milo took the serum for himself, and he’s the one who killed the nurse. Morbius goes into vampire mode and breaks out of the facility, then watches as Milo becomes a vampire and kills a man at a newsstand. After being found, Milo attempts to convince Morbius to join him as they can give in to their newfound powers and urges. He chases Milo into the subway, where they both fly and crash in front of others. Police show up to arrest Milo, but he slaughters them all. Milo attempts to catch Morbius, but he escapes through the tunnels.

After Martine is released from the hospital, Morbius finds her and explains his condition to her and how he has to keep it under control before he succumbs to his bloodlust like Milo. He later finds another lab run by counterfeiters and scares them away in order to continue working and develop a compound to undo his vampirism, even though it will kill him.

Milo goes out to a nightclub where he ends up crossing paths with an aggressive guy. He later follows the guy and his friends down an alley where he kills them all. He later observes Morbius working with Martine and watches them kiss, knowing he has found a weakness in his brother.

After Stroud and Rodriguez find the dead clubgoers, they see surveillance footage showing Milo’s face, making them realize Morbius is not their killer. After seeing this on the news, Nicholas goes to visit Milo and speak to him, but Milo argues that Nicholas always saw Morbius as the favorite son. He attacks Nicholas and leaves his gravely wounded.

Morbius meets with Martine one more time but is alerted to what happened with Nicholas. He goes to be by his side just as he dies. He is later called by Milo, who has kidnapped Martine. Morbius reaches her, but she is also seriously injured by Milo. She lets him take her blood to go after Milo, but a small drop of his own blood falls into Martine’s mouth. Morbius becomes more powerful as he goes to face Milo. He summons his bats and uses them to surround Milo, giving him a chance to approach his brother and inject him with the compound. Milo starts to die but remembers that Morbius gave him his name. Morbius stays by his brother’s side as he dies.

Morbius flies off into the night, while Martine appears to reawaken as a vampire.

During the credits, we see the multiversal rift from “Spider-Man: No Way Home” open up, and Adrian Toomes (Michael Keaton) ends up in this universe. After he is free on the streets, he finds his Vulture suit and locates Morbius. He tells him that Spider-Man is involved in whatever is happening, and he is looking for Morbius’s help in putting together a team to go after Spidey.

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Dr. Michael Morbius suffers from a blood disease. In his efforts to find a cure, he develops a serum that mixes vampire bat DNA with human blood, curing his ailment but giving him vampire-like powers and a strong thirst for blood. His adoptive brother Milo ends up taking the serum for himself, as he also suffers from the disease, but Milo gives into his urges and becomes more monstrous than Morbius.

Milo kills their adoptive father, Dr. Emil Nicholas, and he kidnaps Morbius's girlfriend, Martine Bancroft. She is gravely injured but lets Morbius take her blood to go after Milo. Morbius injects Milo with a compound that undoes the vampire effects and kills him. Morbius flies off into the night, but Martine reawakens as a vampire since Morbius's blood fell into her mouth.

During the credits, Adrian Toomes is sent to Morbius's universe after the events of "No Way Home", and he approaches Morbius to potentially organize the Sinister Six to go after Spider-Man.