It looks like a trivial enough incident: a would-be petty thief makes his escape before he has stolen anything. But when the beat constable arrives to look for damage, he finds something he hasn't been expecting - a dead man, with a wound in his back made by a broad blade ... possibly a spearhead.

Scotland Yard get to work, following what turns out to be a very complicated business, especially when they find they are on the trail of smuggled diamonds leading all the way to South Africa ...