May 1941. At four in the morning, a rust-streaked tramp freighter steams up the Tagus river to dock at the port of Lisbon. She is the Santa Rosa, flies the flag of neutral Spain and is in Lisbon to load cork oak, tinned sardines and drums of cooking oil bound for the Baltic port of Malmo.

But she is not the Santa Rosa. She is the Noordendam, a Dutch freighter under the command of Captain Eric DeHaan. She sails for the intelligence division of the British Royal Navy and is involved in a secret mission.

On board are a Polish engineer and British spy, Spaniards who fought for Franco and Germans who fought against Hitler. For them, this is a last desperate flight to freedom.