Ep 6. Demons

In Castle season 4 episode 6 titled "Demons", the team investigates the murder of a young woman who is found dead in her apartment. The victim, Sarah, was a member of a support group for survivors of violent crimes, and the investigation quickly uncovers a tangled web of secrets amongst the group members.

Castle and Beckett soon find themselves delving into the personal lives of the individuals in the support group, some of whom have troubled pasts and are wrestling with their own demons. They include a former soldier suffering from PTSD, a woman stalked by an ex-boyfriend, and a man haunted by the memories of his sister's brutal murder.

As the team progresses in their investigation, they begin to suspect that Sarah's murder might have been a case of mistaken identity. However, their theory is soon challenged when they receive a message from the killer, who taunts them and implies that there may be more victims to come.

As the case takes a sinister turn, Castle and Beckett race against time to identify the killer and prevent any further harm. Meanwhile, Castle also grapples with his own demons as he struggles to come to terms with the fallout from his previous relationship.

With high stakes and plenty of emotional drama, "Demons" is a gripping installment of Castle that will keep viewers on the edge of their seats until the very end.