No Friendly Drop

At first it seems that Lord Henry Grayle has taken an overdose of sleeping medicine, but the autopsy reveals a tiny amount of scopolamine along with the draught - harmless in itself, but fatal when mixed . . . A poisoner with apparently expert knowledge is at work in the great house at Tassart. But from what motive, and how? Before he can find an answer to these questions, Detective Inspector John Poole is faced with a second, more horrible murder. And when there are shocking revelations both above and below stairs, Poole starts to see light breaking on the horizon.