When the bodies of a number of babies are found scattered around Islington, Detective Sergeant Best is sent undercover to lodge next door to a suspected baby farm. He shadows an alleged 'child dropper' onto a Thames pleasure steamer and finds himself caught up in Britain's worst civilian tragedy - the 1878 sinking of the Princess Alice - a horrific experience which will haunt Best forever. Meanwhile, his determination to avenge the death of a young girl he had befriended and save the life of another becomes a crusade.