The Hand of Fear — Gerald Verner

Millionaire Felix Dexon left his London hotel one morning and never returned. Then his American lawyers began to receive hand-written instructions from him to regularly transfer large sums of money abroad, with the cheques made out to himself. The letters and cheques were confirmed as genuine by handwriting experts. But when his suspicious niece asks a London newspaper to try and find her uncle, their chief crime reporter uncovers a vast web of intrigue by a criminal mastermind responsible for a series of horrific murders...