Alistair Greenwood, Regius Professor of Modern History at Cambridge, is host at a luncheon-party. Among his guests is Gillian Adams, historian on a year's Sabbatical from the University of the Pacific Northwest, revisiting Cambridge for the first time since she took her doctorate fifteen years before. Twenty-four hours later Greenwood is dramatically dead and Gillian is doubly as a witness, and as friend of Edward Gisborne, the Scotland Yard detective who finds himself seconded to the investigation of Greenwood's death.