In 2004, a prominent physics professor disappeared from a train bound for Paaris. When his wife receives emails from someone claiming to know the reason, the team reopens the case. Then their boss, DAS Strickland, is warned off by a shadowy Whitehall figure.

A man found murdered in an alleyway seven years earlier is identified on a website about unsolved cries. The team reinvestigates the case, but the man seems to have no past. Meanwhile, job cuts are imminent, and Brian and Gerry fear being downsized