Mystery! on PBS

“Touching Evil III”: Creegan and Taylor (Robson Green and Nicola Walker) are on the trail of that most psychotic of killers: the one who kills by fire. Making things even more eerie: the first victim is found in a mental hospital. After another arsonist-killer tells Taylor that “purification” is the key to the crime, Creegan devises this theory: “Maybe [the killer] sees these people as sinful, then has to cleanse them of their sins.” Meanwhile, Rivers' replacement (Andrew Scarborough) is greeted with not-so-subtle resentment.