Six senior MI6 officers have been shortlisted to be the next head of British Intelligence. One by one, they are committing suicide. But the suicides are not what they seem. They have been forced to take their lives by a supremely clever individual.

Former high-ranking MI6 officer Ben Sign is instructed to identify who is behind the murders. Could it be a hostile foreign intelligence agency? Sign thinks not. He believes the murderer is one of the six MI6 officers who wants to kill off the competition.

With the help of a male former undercover police officer and a female serving Special Branch officer, he scours London and the rest of Britain to identify the serial killer he nicknames "the whisperer". But the whisperer has help: a former special forces assassin, code name "the limpet".

Can Sign find the whisperer and the limpet in time? Who's working against him? Can he protect national security from a psychopath?