Death came aboard with the cormorant.

It arrived on the seventh day of our voyage... This is the secret report of disgraced former Foreign Office clerk Laurence Jago, written on the mail ship Tankerville en route to Philadelphia. His mission is to aid the civil servant charged with carrying a vital treaty to Congress that will prevent the Americans from joining with the French in their war against Britain.

When the civil servant meets an unfortunate 'accidental' end, Laurence becomes the one person standing between Britain and disaster. It is his great chance to redeem himself at Whitehall - except that his predecessor has taken the secret of the treaty's hiding place to his watery grave. As the ship is searched, Laurence quickly discovers that his fellow passengers - among them fugitive French aristocrats, an American plantation owner, an Irish actress and her performing bear - all have their own motives to find the treaty for themselves.

And as a second death follows the first, Laurence must turn sleuth in order to find the killer before he has an 'accident' of his own.