Try This One for Size [rare books] by James Hadley Chase

When Claude Kendrick, owner of a shadily-run art gallery in Paradise City, was approached by Ed Haddon, the King of art thieves, to find a buyer for the priceless icon of Catherine the Great, he thought his greediesť dreams had come true! For Herman Radnitz, the multi-millionaire, was prepared to pay six million dollars. But there was a catch Radnitz wanted the icon delivered to Zurich as part of the deal.

To his joy, Kendrick learnt of a couple travelling to Europe. All he had to do was make sure that the icon was planted on them unawares...the couple in question were none other than Detective Tom Lepski and his pretty wife...