Howard Rookwood, philanthropist and co-owner of a glue factory, is found dead after returning home from a fundraiser. Although the scene suggests he was trampled by horses on their way to the rendering vats, the blow to the back of Rookwood's head was not caused by a horse's hoof. When a short-handled shovel wielded by someone child-sized is finally determined to be the murder weapon, suspicion turns to the boys who work at the glue factory – and one young boy in particular, Charlie, who turns out to be the long-lost brother of Rookwood's adopted daughter, Eva. As evidence starts to stack up against Charlie, Murdoch learns that Rookwood's disgruntled ex-valet had long been receiving hush money from his former boss for keeping a secret – one so repugnant that it would drive anyone to murder.