It's a dark and stormy Halloween night. Billy is dressed as omnisexual Dr. Jack Harness of Dr. Who fame, but nobody recognizes him. Zoe is costumed as a cheerleader. Rivai receives a strange encrypted message, and the team scrambles to identify the sender. When a scary zombie flashes across their screens, everyone laughs at Mike's Halloween prank.
On board the cargo plane headed for SSC, KITT doesn't understand how Mike can take pleasure in tricking others. Mike offers Sarah a present, but she doesn't trust him. He unwraps a Halloween snow globe, and Sarah moves in for a kiss, until a spider crawls out of Mike's mouth! Graiman has plans to get Mike back for a childhood Halloween prank, and freaks Billy out with a mechanized severed hand.
In preparation for that night's Halloween party, KITT has costumed himself as a Warrior in Pink Mustang. Mike thinks KITT should have dressed up as a vampire instead. The discussion comes to a halt when KITT detects Sarah and Mike's dramatic hormonal increase. Why can't the two of them get it together?
Graiman and Zoe do rounds, surprised to find a tech lying on the floor of the mainframe room. They think it's another one of Mike's jokes until Zoe realizes the guy is really dead. It's an internal breach. The lights go out and three shots are fired. The SSC immediately goes into lockdown, which, KITT informs Mike and Sarah, means all external communications are suspended.
As the airplane ride gets bumpy, Sarah tries to override the non-comm protocol, explaining that there must be a back door built into the program. KITT thinks that the presence of the back door means Sarah is deceiving the other team members. Sarah and Mike are thrown to the back of the plane. When his restraints come loose, KITT has to think fast to avoid crushing them without ripping a hole in the plane.
Zoe tells the team what happened. When the lights went out, she dove to the floor, knocking Graiman out cold. Billy pulls up all surveillance footage from the crime scene, but can't detect a shooter. Soon he realizes that the cameras have been disabled; there's a video loop in their place. As Graiman is wheeled out on a gurney, Zoe plants a fat kiss on Billy, amazing him.
KITT asks Sarah if there's a back door programmed into him, but she refuses to answer. Mike thinks Sarah has hurt KITT's feelings and should apologize. Sarah admits, she doesn't know why her father programmed a back door into KITT, but if he'll help re-establish contact with the SSC, he can ask Graiman himself.
Billy gathers digital sound waves to make the shooter's audio fingerprint. Graiman regains consciousness to inform them that KITT's self-destruct program was activated by the shooter. Torres is incensed that the self-destruct program exists. Graiman explains that he had no choice - they can't risk KITT turning into KARR. KITT will blow up in 20 minutes, and the cargo plane is 1000 miles out at sea.
When Sarah hacks through the back door of KITT's comm system, Graiman tells them the bad news. The only way to de-activate KITT's self-destruct program is with the digital hand scan of whoever activated it - the shooter. Sarah knows they're on their own, and KITT can't help but feel betrayed, even if he's not capable of emotion. He thinks the only way to save Sarah and Mike is to jettison himself from the plane.
As Rivai observes, Billy separates his recreated sound waves, isolating that of the shooter. Now he has to match the pattern against the voiceprints of 1700 employees. Rivai figures that they can cut search time if they can determine the sex of the shooter. Zoe offers ballistic evidence indicating that the shooter was a woman, about 5'5" tall. Everyone is shocked when the Billy's voice print identifies Rivai.
Thinking that KITT's shell is expendable, Zoe suggests that they download his files. Graiman tells Sarah to get that ball rolling. Sarah points out that KITT's neural network or thought process can't be downloaded, which means that his "memories" will be reduced to raw data, with no attachment or significance. Claiming he'd rather not be saved, KITT refuses to begin the download.
Having lost his memory, Mike can relate, and promises KITT that he and Sarah will help bring his memory back. Back at the SSC, Graiman can't believe that Rivai is the shooter and insists she's been set up, but Zoe brings up more damning evidence. Torres takes Rivai's gun and confines her to a guarded pod. Graiman and Billy try to check video surveillance to clear Rivai, but it's all been wiped from the system.
Mike can't believe that Rivai is the shooter, but KITT's not so sure, considering all the Halloween pranks. Sarah thinks they might be able to de-activate KITT's self-destruct manually, by dropping the engine and pulling out his propulsion system. KITT knows there's not enough time, but Mike gets started, as KITT replays his favorite memories for what may be the last time.
Billy and Graiman realize that Carrie's voice print was manufactured - most likely by someone who knows all about the SSC. Just then, the fire alarms sound, coming from Carrie's pod. Graiman orders Zoe to open the doors, but Torres insists on maintaining full lockdown. He doesn't care if the SSC burns to the ground, they have to find out what's going on.
KITT volunteers that the possibility of self-programming may have led Graiman to gave him a back door. Sarah claims self-programming is impossible, but KITT knows that his prototype, KARR, had that capability. KARR is a cybernetic exoskeleton programmed for self-preservation, or as Mike puts it, a killer robot. When Mike sees images of KITT, he has a dÃ©jÃ� vu, kind of like he already knows KARR.
Graiman puts Rivai's hand on a tablet scanner rigged to stop KITT's self-destruct, and it doesn't work, proving she's not the shooter. And there is no fire in her room; the shooter is setting off random alarms across the complex. Torres gives Rivai back her gun, and the team runs to the main frame room to see if the shooter is still in there. They don't find the shooter, but they do find the real Zoe, bound and gagged.
Mike realizes that the whole exercise has been a diversion, to force them to download KITT's files. Now it's too late, and to preserve their lives, Mike and Sarah will have to dump KITT off the plane. Imposter Zoe aims her gun at Billy, pulls him into the entry tunnel and forces him to a keypad. Torres and Rivai train their guns on Imposter Zoe.
When Billy asks if it's all been an elaborate Halloween prank, Zoe instantly knows how to save him. She races to the vent over his head, and drops into the tunnel to disarm Imposter Zoe. Meanwhile, the cargo door on the plane malfunctions. KITT claims the window to jettison him has passed, telling Mike and Sarah to prepare to jump.
Graiman rushes up to Imposter Zoe with the scanner tablet, managing to de-activate KITT's self destruct program in the nick of time. Torres asks Imposter Zoe who she works for. Suggesting he should ask himself the same question, Imposter Zoe bites down on a capsule, committing suicide.
Torres tells Graiman that Imposter Zoe was employee Teri Lee, who underwent surgery to impersonate Zoe. It's all in Washington's hands now, and Torres has redoubled security. Graiman points out that only three neural networks support KITT: KITT, KITT's back-up, and KARR. The only explanation for the whole thing - KARR's still out there. If someone succeeded in putting KITT's brain into KARR's body, they'd have the ultimate weapon.