Crabtree refers pre-teen fatherless Alwyn Jones, who reports having seen a giant silver knight by the river, so Murdoch, who goes check and brings the cutie home to his mother Enid Jones, just what he needs now Julia seems out of the picture. Later retired mathematics professor Ezra Delamore, employed by machines industrialist Martin Hammerton, is found poisoned with Pruissian acid, by ingenious injection by a fake blind man's cane. Government spy Terence Meyers requires police help to solve the murder, suggesting the killer be elusive Prussian spy Kaspar Bomgaarts. Ezra's notes, partially confided to his maid, and examination of the firm and government interest prove useful when Alwayn goes missing and the 'silver knight' he saw turns out a military robot prototype, which William believes impossible even before a dwarf's corpse is found in the river.
—KGF Vissers