It's a lovely day in Chicago where, following a lecture on love, Dr. Daniel Pierce spends a portion of the afternoon in bed with his psychologist-turned-lover Dr. Caroline Newsome and the hallucination/best friend based on her, Natalie Vincent. After his 'lunch' and back at the university, FBI agent Kate Moretti arrives with a new case for Daniel to consult on. A woman, one Ellen Resnick, has reported the abduction of her husband Preston - by aliens from outer space!
They make their way to the Resnick residence posthaste, and ring the bell, which summons a flustered Ellen to the door with the melody from Close Encounters of the Third Kind. Their initial interview is cut short when Preston emerges from the house, whom she insists is an alien dopplegänger.
Preston describes Ellen as having been a little paranoid recently. She repeatedly thought a car was following her, though it was a different brand each time. The most recent time, she got spooked and crashed her car into a telephone pole. Daniel diagnoses her with Capgras Delusion, explaining that the connection between the emotional center of her brain, and the Visual Cortex has been severed. When he came home at night, she recognized her husband's voice, but by the light of day awoke to see a stranger in bed. Preston, being a science-fiction author caused her to fixate on aliens. Daniel convinces her to go to the hospital for a brain scan, just in case there's a pesky alien microchip implanted in her brain.
At the hospital, Daniel meets Gerry and Barbara Bruckner, friends of the Resnicks. He explains to them and Preston that the car accident caused an aneurysm to rupture, damaging her Occipitotemporal region. If Preston wants to speak with his wife, it'll have to be via phone. Also, Barbara is an alien.
During a call Preston makes to Ellen from their house, their distinctive doorbell is rung. He lies to her about the doorbell, saying the sound came from the TV. Ellen senses something wrong, returns home, and is subsequently found kneeling above her dead husband, knife in hand, covered in blood. "Don't worry", she says. "It's the alien. It's not my husband!" He was already shot dead on arrival, so she decided to do an impromptu alien autopsy to prove she didn't murder her husband.
Preston's publisher reveals that rival author A.Z. Weyland threatened her and Preston. He accused her of giving Weyland's manuscript to Preston who he claims used it as the basis of his new novel. He's currently at a book signing, so the duo rushes off to the Far Beyond Con Chicago, where frantic cosplayers abound. When an announcement triggers a stampede, Daniel seeks the calm of an elevator. A man compliments him on his Doctor Who costume, introduces himself as Gorthar from Tau Ceti 5, a shapeshifting alien, and Daniel's newest hallucination.
Kate introduces herself to Weyland, launching him into a public rant about the military-entertainment complex and the FBI trying to silence his non-fiction tell-all alien book. He then tries to run, but is quickly stopped by stormtroopers. In interrogation, he claims aliens at his bedside with a paralysis beam as his alibi. Daniel, with some inspiration from Gorthar from Tau Ceti 5, interrupts the interrogation insisting Weyland is innocent and suffers from narcolepsy and sleep paralysis. Just as he finishes making his case, the results on a gun found at Weyland's apartment come in and is revealed to be a match to the bullets dug out of Preston's corpse.
Back at the convention, a Slave Leia speaks at Preston's memorial. Ellen is crying, which doesn't make sense if she believes her husband is still alive. She refuses to talk, and now Gerry's an alien too. Hallucination/best friend Natalie wonders why the guy who yesterday was Just Gerry is now an alien. Suspiciously, Ellen developed an emotional connection to Jerry over night.
In interrogation, Gerry eventually says he won't talk without a lawyer then, as Daniel and Kate play good-cop/bad-cop, immediately starts expositioning. He was stalking her in rental cars, and was responsible for spooking her into a telephone pole. Having feelings for Ellen, he decided it was the perfect time to move in on her, what with her husband being an alien and all. He killed Preston, and framed Weyland. He then told Ellen that he killed the alien and, admitting that Preston is dead, seduced her.
In b-plot land, Kate, wanting her divorce papers signed, is blackmailed into a birthday picnic with her husband's grandmother. Despite them not telling her, Grandma finds it obvious that they're getting divorced, and privately tells Kate a story to suggest that Husband Donnie can change. Afterwards they sign the divorce papers. Meanwhile, Caroline is suspicious that Daniel is off his meds, discovers that he is, overhears him talking to her hallucination counterpart, and breaks up with him.
Back to the lecture at the beginning of the episode, Daniel wraps up the ending. The trials and tribulations of love, he argues, are worth it. Even just the memory of a fulfilling relationship will leave us never truly alone.