 Joseph Rearden, a British Intelligence agent, arrives in London and makes a rendezvous with Mackintosh, the head of his organisation, in a discreet office located just off Trafalgar Square.Mackintosh and his deputy, Mrs Smith, inform him of a simple way to steal diamonds which are transported via the postal service to avoid attention.This he does, apparently getting successfully away after punching a postman, and making off with the diamond-filled parcel.