The last thing Jason Roth expects when he arrives home at midnight is to find a beautiful young woman rummaging through his desk. She's sorry, claims she made a mistake and isn't doing anything wrong. She thought she was in someone else's apartment.
Marielle Delaney claims to be searching for some missing papers, and since she has the key to the apartment, and it's probably from its lawful occupant, her only mistake was to enter the wrong apartment, surely a forgivable offense. It's not her fault the key opened the wrong door, and she is very sorry.
Jason doesn't quite buy her story, but before he can get to the bottom of her strange break-in, the phone rings and she slips out while he is talking to his caller. A few hours later she is at his door again, visibly distraught and asking Jason to help her find the way down the stairs of the unlit building. When they reach the building entrance, they see a taxi idling at the front door. A closer look reveals a slumped body in the back seat. Then before he can say or do anything, Marielle disappears into the night and Jason is left to deal with the authorities on his own.
Although he has no reason to protect her identity, Jason does. Thinking that no one else knows about her late night visits, Jason decides not to tell the police about the woman who broke into his apartment and whom he escorted out of building hours later on the night Morris Barnes was murdered. It might have ended there except a shady lawyer, another witness, and the victim's brother start asking questions about Barnes, his murder and the source of his income. Jason can't get a good night's sleep worrying about the implications of his silence, nor can he forget his encounter with the beautiful Marielle. He quite unexpectedly discovers who she is and a chance encounter leads him to her. While she is grateful he covered for her during the investigation of the murder, she's less than happy to run into him again. Emphatically she tells Jason she doesn't want his help or his attention. Fortunately for Jason, Marielle is staying with a friend who is terribly bored and invites Jason to join them for a fun night on the town. Jason jumps at the opportunity and Marielle grudgingly goes along.