Following several months abroad, Judge Dee Ren Jie has returned to the city to foil a transaction between a Russian diplomat and a Japanese mercenary. Aided by Lao She --- the Watson to his Holmes --- along with several other colorful characters, Dee stops the illicit sale of an extremely valuable “dragon-taming” mace. The mace’s owner is a Chinese businesswoman who thanks Dee for its retrieval by throwing a lavish dinner party. In attendance is British banking official A. G. Stephen, who argues with the group about the tenuous state of Chinese nationalism --- and is poisoned two days later. Dee knows this cannot be a coincidence, and suspects Stephen won’t be the only victim. Sure enough, a young Chinese communist of Lao’s acquaintance is killed not long after --- and a note with a strange symbol is found by his body.

London, 1924. When shy academic Lao She meets larger-than-life Judge Dee Ren Jie, his quiet life abruptly turns from books and lectures to daring chases and narrow escapes. Dee has come to London to investigate the murder of a man he’d known during World War I when serving with the Chinese Labour Corps. No sooner has Dee interviewed the grieving widow than another dead body turns up. Then another. All stabbed to death with a butterfly sword. Will Dee and Lao be able to connect the threads of the murders --- or are they next in line as victims?