Amanda Collier is the daughter of David Collier, who had a history of mental illness. Some time before the events of the episode, police had David as part of a lineup, as they were searching for a serial killer. Three witnesses--Val Butler, Jason Bennett, and Mark Heller--were all pressured by police to finger a suspect, and they pointed the finger at David. David ended up imprisoned, but at midnight on the third night of his jail time, he smashed a light bulb and used the wires to electrocute himself, committing suicide by stopping his heart.
David's suicide was due to his inability to deal with the accusations against him; accusations that were incorrect due to a man named Nigel Malloy being the actual killer. As for Amanda, she suffered a mental breakdown a year prior and became vengeful against the people she blamed for her father's death.
Amanda's first victim was Val, and she began her plan by moving in with Val and becoming her roommate. This was done to get closer to Val and gain info on the others, and afterwards, Amanda sent an odd DVD consisting of various eerie symbols and an ominous voice stating that Val would die at midnight in the third night. Sure enough, Val died that very hour, but it was at the hand of Amanda, who used a modified taser to commit the murder. The villainess disoriented Val with the taser's light, and then electrocuted her to cause her heart to stop; the same fate as David. Amanda appeared at the scene and acted as a shocked roommate while speaking with Richard Castle and Kate Beckett, but later on, the evil Amanda did the same to Jason, as he was found dead in the same way.
Castle believed that an evil spirit was killing both victims, due to Val's books about spirits and the good luck charms in her apartment. After Nigel Malloy was mentioned, as well as the revelation that he had since passed on, Castle's new belief was that Nigel's spirit was out for revenge. Even after Castle and Beckett visited Nigel's brother, Leopold, it was believed that the deaths were connected to someone with a history with the Malloy brothers. When Mark was revealed to have received the DVD, Castle and Beckett found him at an undisclosed cabin, as he was hiding out after watching.
Beckett left to find out who was outside the cabin, only for that someone to be revealed as Nurse Lockhart, who tended to Leopold. Lockhart was not the killer, as she stated that she was there to save Mark from the actual murderer. Meanwhile, Mark revealed everything to Castle, including David having a daughter--named Amanda. When Castle realized that Amanda was the name of Val's roommate, he came to the conclusion that she was the actual killer, and afterwards, Amanda's reveal was confirmed when she entered the cabin searching for Mark. The demented murderess stated that Mark's time was up, adding that the three days were all that he gave her father, only to find Mark with a gun-wielding Castle. Amanda subdued Mark and Castle with the taser's light, but just as Beckett entered the cabin, Castle knocked out the villainess with a jar of holy water. Amanda was later arrested (off-screen).
- "Your three days are up, Mark. The same three days of fear my father had." (Amanda Collier's ominous warning to Mark Heller during her attempt to kill him)