New Year 1795, and Laurence Jago is aboard the Tankerville mail ship, en route to Philadelphia.

Laurence is travelling undercover, supposedly as a journalist's assistant. But his real mission is to protect a civil servant, en route to Congress with a vital treaty that will stop the Americans from joining the French in their war against Britain. When the civil servant meets an unfortunate - and apparently accidental - end, the treaty disappears, and Laurence realises that only he can keep the Americans out of the war.

Trapped on the ship with a strange assortment of travellers including two penniless French aristocrats, an Irish actress and a dancing bear, Laurence must hunt down both the lost treaty and the murderer, before he has a tragic 'accident' himself...