John Thorneycroft, forensic psychiatrist, witnesses young Ben Tifflin consume sherbet that has been laced with aspirin at a world famous delicatessen. Thorneycroft gets the boy to hospital in time to save his life, but a few days later he is informed by DCI Liam Connor that there had been another, and fatal, attack. Jock Robbins, public benefactor, had died from eating poisonous mushrooms supplied by the same delicatessen. Jock's sister receives a card bearing the number 5. The Tifflins receive card number 4 and a third victim is sent card number 3.It seems a poisoner is committing serial attacks with a view to destroying the delicatessen's international organisation. Thorneycroft joins the police investigation as a consultant and comes to believe the attacks could be aimed not at the rich and powerful Lenards who have made many enemies. Will victims 2 and 1 be chosen from their ranks? Will Thorneycroft and Connor identify the poisoner before the Countdown Murder is made complete?