To Russia with.... Panache

Jason is abducted in order to help the Moscow police work out how three men on a workers' delegation, got into a lift and then, when the doors opened again, there was nothing left of them but three piles of ashes. He discovers that they made their exit from the lift by means of a trap door, but comes to appreciate that they are part of a larger plan to tunnel into the Kremlin to steal art treasures.