On a visit to Belgium, married couple Bob (Hugh McDermott (actor) ) and Susie Westlake (Honor Blackman) become involved with wealthy financier, Steve Mordaunt (Ivan Samson), in the sale and transfer of a collection of rare books. In an attempted burglary at Mordaunt's home, his love interest, Mrs. Rosemary Delgado (Jane Hylton), is suspected. She was once romantically linked to a gangster and she leads the Westlakes in a search for Achemd's writings, a middle eastern 14th Century seer which has inspired an extreme political group, and thought to be in the collection of rare books that Mourdaunt now owns.