HMS Duncan is deep in the heart of the Black Sea as it heads towards Crimea, when a Russian ship it has been tracking suddenly disappears. Pilots Johnny Hamlyn and Tim Dunning take off in a Wildcat helicopter and discover that it is a spy ship, probably on a mission to monitor the Duncan. The situation soon escalates as Russian jets start circling the Royal Navy ship, and Commodore Mike Utley and Captain Eleanor Stack must assess the situation and consider how best to protect their personnel