CASSANDRA by David Morrison

1941. In the north Atlantic, as British merchant shipping is suffering at the hands of German U-Boats, staff at Bletchley Park try to decode enemy naval messages sent using Enigma cipher machines. A new girl working in the Registry Office, claims to have a special ability which can help – and promptly disappears. Is her claim true? Has she become the victim of infiltrators determined on silencing her, as the clock ticks on the fate of a large convoy?