Lt. Brevet Cable, RN--hero of Callison's earlier A Plague of Sailors--returns here in a more conventional naval thriller in which he tries to defuse an international incident on the high seas. The plot is less compelling, and Cable less amusing, this time, but Callison tells the story in workmanlike fashion. For the record, I prefer the UK title (A Frenzy of Merchantmen) to the US title (An Act of War). ( )