Amy Thomas was the main antagonist of the 2016 Lifetime TV film Unwanted Guest. She is portrayed by Kate Mansi, who also played another villainess Krystal Kellers in the following Lifetime film, Boyfriend Killer.
Not much is known about Amy's past, but at the end of the film it was revealed she wasn't born as Amy Thomas, as the real Amy Thomas died two years before the film events. She was a college student and roommate of protagonist Christine Roberts (played by Valentina Novakovic) Also prior to the movie's start, Amy killed student Allen Curwood by hitting him over the head and showing him down an outdoor set of stairs, making it look like it his death was accidental when police and detectives were questioning the latter.
As Christine prepared to leave for winter break, Amy claimed her parents were out of the country, causing Christine to invite Amy to her home. Once they arrived, Amy acted politely with Christine's mother, Anna, and her stepfather, Charles (whom the latter develops a sudden attraction to him) Amy then shows her true villainous colors (albeit subtly and unknown to Christine and her parents at first) by drugging Christine's wine. The next morning and a changed look of Amy she made breakfast for the family and furthered her attractions with Charles. Later on in the same day, Amy returns to the college to murder Allen's girlfriend Marilyn by going to her dorm room as Marilyn was packing up for departure by bashing her head with a wine bottle she picked up from the Roberts' house and hid her body in her college dorm bed. After that, and sabotaging Anna's real estate work, Amy once again drugged Christine and left her for sickness by leaving the window open, she then puts on a pink lingerie and goes to the living room to share wine with Charles in an attempt to seduce him, which Charles was originally oblivious to her seduction and flirtation attempts. The next morning, the Roberts house received a call from the detectives investigating Allen's death and asking about Amy, Amy posed as Christine and claimed Amy has left the Roberts' house. She then came across Christine's recently escaped gerbil, Mr. Chips, and kills him by bludgeoning him with a wooden pepper grinder.
The next scene, Amy was helping Anna to prepare for a company dinner party for Charles's work, Amy purposely pushes the stool under her as Anna was reaching for a pot, causing her to have a broken leg. With both Christine and Amy out of the way, Amy became more aggressive and obsessive in her pursuit of Charles. Anna, now becoming suspicious of Amy, told Charles about how she felt especially informing him that Amy is after Charles by getting her and Christine out of the way, she was eventually able to convince him to get Amy out of their home somehow. Right before the company dinner party, Amy tried to seduce Charles into kissing her. But he rejected her, upsetting the villainess. Amy also earned the attraction of Charles' co-worker Ken, but after learning that Ken had talked with the detective investigating her, Amy kills him by removing the brakes on his car. The next morning, having found Anna after Amy drugged her food and Christine was not getting any better, Charles told Amy that he was hiring a live-in nurse, essentially kicking Amy out. An upset Amy went into a rant against Charles and his family before agreeing to leave.
At work, Charles was confronted by the detectives investigating Amy's crimes at work, and they informed him on how dangerous Amy truly was. Meanwhile, at the Roberts' house, Amy was lecturing Anna on how she finally found "love" with Charles and deserved to give her a lethal injection. Before she carried it out, she was interrupted when Christine called for her from her bedroom. Amy then took Christine out of her bed, first saying she was taking her to the hospital before revealing her true self. She and Christine got in a brief fight before Amy forcibly dragged Christine in the kitchen, she then goes on a diatribe about how Christine and her family are "ungrateful" and that she had nothing. She then knocked Christine out with a frying pan and places her face on an open and running stove to die of carbon monoxide, but soon failed when Christine barley regained conscious. As Amy was about to kill Christine with a knife, Anna ran out from the hallway and injected her with the syringe Amy accidentally left in her room, Amy then pushes Anna to the floor and prepares to finish them off just as Charles and the detectives arrive, who told her to stand down.The deadly psychotic girl apologizes to Charles before she collapses to the floor, having giving in to the drug's deadly effects.