In January 1938, a young man is found shot dead in the garden of the West London house where he is a lodger. Within days, two more men of similar age are murdered in the same area. The circumstances are almost identical in each case. A small-calibre weapon had been used – and given the absence of noise, it was almost certainly fitted with a silencer.

Chief Inspector Adair investigates. Clearly, a serial killer is at large, and the newspapers are full of ‘Jack the Ripper’ references, with innuendos about the competence of the police.

Then a fourth man is found. This time, the pistol is still in situ, the man’s thumb on the trigger, and the muzzle – with silencer – in his mouth.

Who is he? Why did he kill the other men? And given that the police have no idea of his identity, he clearly didn’t commit suicide because the police were close on his trail. Remorse, perhaps? DCI Adair’s task is not yet complete.