Each year, for five years, a nanny - and the child she was with - has disappeared around the same time each year.

Subsequent to their capture, they are sexually assaulted, tortured and then murdered by being drowned in scalding water.

The children they were with were left at a hospital or church, unharmed.

Each year, on May 13, their bodies are left in a park.

In the case of the latest victim, the Unsub has decided to hold onto both the nanny and the child she was with, the latter of whom suffers from asthma.

The Unsub is classified as a sexual sadist with rage issues.

The team discovers who he is through the help of one of his victims who managed to escape.