Shakma

Sorensen injects Shakma with an experimental variation of corticotropin intended to inhibit aggression. The baboon awakens and lashes out, going berserk. Sorensen orders Sam to euthanize him, but Sam cannot bring himself to do it, leaving Shakma unconscious.

Sorensen insists on performing a necropsy on Shakma the following day, keeping the animal alive for study. He overrides any disposal plans, ensuring the animal will remain alive until the necropsy. Sam and others are kept in the dark about the plan.

Sorensen organizes a live-action role-playing game for Sam, Gary, Bradley, Richard, and Tracy. The objective is to reach Richard's younger sister Kim on the top floor, and players are issued walkie-talkies that connect only to Sorensen as gamemaster.

Sorensen disables the fire alarm system and locks the offices and the building to prevent anyone from leaving until the game ends. This creates a controlled, claustrophobic environment that heightens the tension.

Shakma regains consciousness and kills Bradley when he ventures into the fifth-floor specimen room. The group realizes something is seriously wrong as disappearances begin to mount.

While investigating Bradley's disappearance, Richard is killed under Sorensen's orders. The gamemaster's control over the events shows how far the game has spiraled out of control.

Sorensen investigates the disappearances and finds Richard's mutilated body. He is then attacked and killed by Shakma, signaling the shift from manipulation to direct danger.

The sounds of carnage alert Sam and Tracy to Shakma's presence, but they cannot use the elevator because Sorensen's body jams the door. They decide to move upward via the stairs to continue the search.

Tracy goes to the electricity lab to fetch a strobe light and uses it to temporarily blind Shakma. She also holds the specimen room door shut while Sam goes to locate and remove Sorensen's body from the elevator.

Tracy confirms Richard's presence in the specimen room and distracts Shakma while Sam attempts to recover Richard's body. Shakma returns before Sam can recover, forcing another narrow escape for the pair.

Gary is killed while using the elevator, allowing Shakma access to the upper floors. Tracy is killed soon after in the sixth-floor restroom, further heightening the danger.

Sam climbs toward the top floor to warn Kim, keeping Richard's fate from her for the moment. He arms himself with a kitchen knife in case Shakma confronts him, while Kim writes a note to Sam and prepares to act.

Kim finds Richard's body on the top floor but is killed by Shakma in the process. The loss compounds the survivors' desperation as they face a now all-out threat.

Sam discovers Bradley's and Kim's bodies and contemplates alerting the police from Sorensen's office. His grief over Tracy's death fuels a resolve to kill Shakma himself.

Sam sets a trap to electrocute Shakma, but the creature evades it and mortally injures Sam. He lures Shakma into the incinerator and Shakma is burned to death as Sam collapses, saluting a nearby monkey doll and uttering 'I win' before dying.