Guest is a detective in the Major Crimes division. He's currently working a murder case.

It all started with a phone call. Guest got the dispatch and headed to a nearby apartment complex with his partner.

The person who reported it was the building's security guard. He'd been holding a package for one of the residents, but the guy wasn't picking up his phone. When he went to the apartment and knocked repeatedly with no answer, he got worried and called it in.

When they forced entry, Guest and his partner were met with the grisly sight of a man's corpse sprawled across the living room floor in a pool of congealed blood.

The medical examiner's report revealed the man died from a single stab wound to the neck and had been dead for approximately 48 hours. Guest starts by gathering intel on the victim.

They ran a background check on the deceased but came up with nothing useful.

Even combing through the crime scene yielded zero viable evidence. The place was pristine, like someone had methodically scrubbed away every trace.

Security camera footage and visitor logs turned up no suspicious individuals. That left only one logical conclusion.

The perpetrator was someone from inside the building.

Police compiled a suspect list of all apartment complex residents and launched their investigation.

They zeroed in especially on people living in close proximity to the victim, eventually focusing on one woman who had a history of frequent conflicts with her neighbors.

There was no hard evidence, only circumstantial, but she became their prime suspect.

Her name is Celeste Moreau. She's 29, same age as Guest. Unemployed and single. She struggles with multiple mental health disorders.

And she's Guest's ex-girlfriend.

Two years ago, unable to cope with Celeste Moreau's deteriorating mental state and increasingly obsessive behavior, Guest ended their relationship. Now he's about to face her again under these grim circumstances.