Mannering's assistant,David Marlowe,is abducted from the shop and a ransom demanded for his return. Specifically the ransom money is to be obtained by Mannering selling a fake Renoir painting to art collector Sir Richard Ellacott. On Templeton-Green's authority Mannering sells the painting and obtains the money,which is to be delivered to Sir Richard's nephew,Roddy. Mannering knows that Roddy is one of the kidnappers but must be careful not to put David's life at risk.
—don @ minifie-1