When a teenager and her sister are the sole survivors of the gruesome murder of four members of one family in a quiet suburban neighborhood, Grissom and his entire team investigate the crime. What initially looks like a bizarre cult murder becomes more disturbing when they discover the motive behind the massacre.

At a swanky fundraiser, attended by the sheriff, a woman turns up dead in the pool. The owner of the house is away and a young couple is housesitting. Warrick looks into an apparent professional hit in the glass elevator of one of the hotels.

The whole team must investigate a crime where a husband and his porn star wife were murdered execution style. Things get personal for Catherine when Grissom talks to her about her evaluation. Brass believes that Sara may have some type of problem.

The CSI team investigates a fire at a music venue that leaves four people dead, including two band members.