on a visit to belgium, married couple bob (hugh mcdermott ) 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.