Jenny Sears, a hard-working, divorced mother of two, is a strong-minded, independent woman succeeding in the tough business world of London, 1900. Captain Nick Blackburn, badly wounded in action, has just returned home, though he has no memory of who he is, just where 'home' might be. A twenty-year veteran of the London Police, Wilfred Pool has dealt with the worst, most vicious criminals the city has to offer. Increasingly weary, cynical, he is thrust into a new investigation involving a rash of gruesome murders resulting from the appearance of a precious 'Black Diamond' within the underworld realm he knows all too well. When Jenny is caught up in an abrupt, violent encounter with her current suitor, a volatile gypsy named Felice, to her astonishment she is helped, protected by a randomly passing Nick Blackburn, a man she was once deeply involved with years ago, but who now doesn't recognise her, has no idea even who he is himself. Ruthlessly pursued by Felice, himself a prime suspect in Pool's investigation of the Black Diamond killings, Jenny finds her life starkly threatened by the suddenly treacherous present, at the same time unexpectedly confronted with the uncertain reappearance of a ghost from her past, a man forgotten in every sense of the word.