The Ambassador's Boots

Previously published in the print anthology Partners in Crime. The monogrammed kit bag of the American ambassador to England, Randolph Wilmot, is switched with Senator Ralph Westerman's. Wilmot hires Tommy and Tuppence to find out why. When the senator's valet shows up at the embassy to exchange the bags, they discover that the senator has never heard of this valet, or of any confusion between kit bags. Who is the valet, and why did he need the bag?