In the early 1950s after the war in Europe ex-GI Frank Prior (Lloyd Bridges) takes a flight to London to visit his lover Pauline French (Moira Lister) but as he de-planes a passenger is shot dead and a hunt ensues for a limping man who may have been on the scene. Since Frank was close by when the killing occurred he is pulled into the investigation led by Inspector Braddock (Alan Wheatley) who believes the ex-GI may know something more than he is telling. A well-known sports woman, Pauline is busily selling her high powered speed boat and when she stops to talk with a business associate Frank notices it is a limping man. The Police are interested in Pauline's possible involvement in the killing as she and the assassinated man Kendal Brown (Bruce Beeby) have for the past 6 years been intimate friends. As Frank becomes more involved he discovers that Kendal Brown has been using Pauline and her boat to smuggle contraband into the country. An alluring theatre hall performer Helene Castle (Helene Cordet) posses many pieces of evidence which the police are looking for, and when Frank investigates he discovers some shocking truths about himself and his visit to London.