Find the Clock

'John Chinaman: Take this message at once to Miss Rita Thorne, The Broadbury, somewhere on Independence Boulevard, Chicago. You have letter from London. Secure immediately old alarm clock owned by uncle described in letter. Remember there were two similar clocks, one formerly used by servant. Pay anything to get the right one of the two. Lock it fast in downtown safety vault. Then notify Catherwood you have clock and hold all cards.'

This, written on a handkerchief, caused a search for surely the most elusive clocks in the world!