Holmes and Watson enter the world of nuclear security when they investigate the murder of an ex-Yakuza gang member. Also, Captain Gregson is blindsided by a stunning personal confession from his daughter, Hannah, a police sergeant.

Holmes and Watson find themselves on the hunt for a serial killer after a murder rocks their inner circle. Also, Holmes’ neurological recovery regresses and his sobriety wavers as his commitment to catching the killer grows into an obsession.