Someone has broken into a big London bank and painted a strange Chinese cipher on the wall. Across town, the same cipher turns up at a library. Two men connected with each of these sites are later found dead: a Hong Kong trader and a freelance journalist. Given the height and security of the various buildings involved, only a killer who can scale sheer walls could have done it. And only the master of deduction can solve it: Sherlock.
Sherlock and Dr. Watson soon establish that both men often traveled to China and both met their end shortly after visiting the Lucky Cat Emporium in London. The meaning of the cipher is more baffling, and Sherlock contacts a friendly graffiti artist for help cracking this puzzle. Also helpful is a fugitive museum curator, who herself has received the ominous cipher. And eagerly sought is "the book that everybody owns," whatever that is, which holds the definitive solution to encrypted Chinese messages appearing throughout London.
Complicating the plot, Watson has found a part-time job at a medical clinic and has romantic designs on his boss, Sarah. Their first date - to the circus - turns into a circus of sorts when they confront a life-threatening peril. But not as perilous as the fate that awaits them after Watson is delivered the lethal cipher, under the killer's mistaken impression that he is Sherlock.