Cassy and Jonas make an extraordinary couple with an unusual need - human hearts. With no ties, family or friends, never settling, they head forwards on their eternal journey round the world. While making the crossing from the United States to Europe, unbeknown to Jonas his latest victim emails a recording of his own death to his computer at home. The couple travel to London, where they seek out an old friend but discover disturbing details about his life. Federal Agent Wheeler picks up a case which fits into a pattern he's working on, but the more he searches, the worse it gets and the more mutilated corpses he finds. He follows minor clues and traces until he reaches Charleston, South Carolina where his trail goes cold. Meanwhile, in Liverpool, once he's seen the horrific recording sent by Jonas's vicitim, Detective Silverwood realizes he's working on an international murder case. Together Agent Wheeler and Detective Silverwood team up, and with Detective Tutor, making use of plenty of surveillance equipment, expand the search across England, although the couple do their best to shake them off. Who are these people? Why are they killing in such a regular fashion? Who are they travelling so purposefully to meet? Will modern technology help to catch and stop them? What is their secret?