Interpol are hunting a pair of robbers, an 'engaged couple' targeting jewellery shops. The evidence points to the pair being English, and when one of them is slightly wounded in their latest robbery Duval finds a further clue - a British-made glove with a bullet hole in it. A break-in at a doctor's surgery in Switzerland suggests to Duval an attempt to treat the wound; looking for an English couple, he finds he has an entire coach party of possible suspects.