3. Child Predator

Complete story — includes the ending

Sherlock and Joan investigate the abduction of a young girl by a serial killer known as "the Balloon Man", whose name comes from the fact that balloons are left at the scene of each of his abductions. The Balloon Man targets children. Matters get complicated when the Balloon Man's first victim from 2005, Adam Kemper, is caught by the police. Sherlock deduces that Adam has Stockholm syndrome and sympathizes with him to help find the killer. Adam gets an immunity deal for crimes he committed in consort with the Balloon Man. The Balloon Man is identified as Samuel Abbott, but when the police come for him, Abbott commits suicide. His most recent abductee is saved. However, when Sherlock examines Abbott's home, he finds evidence that Adam is, in fact, the Balloon Man. After Abbott kidnapped him, he managed to turn the tables and dominate Abbott. Sherlock finds a way to bring Adam to justice. One of the murders had to have been committed by Adam alone, because Abbott was in the hospital at the time.