The greatest naval trial in the Georgian period is underway at Portsmouth with the court-martial of Sir Home Popham, Captain Sir Thomas Kydd's commanding officer in the doomed occupation of Buenos Aires.

Kydd has some sympathy for Popham's unauthorised action, but his support for his former commander leaves him athwart some very influential people in the admiralty. With his frigate, L'Aurore, unfit for sea, Kydd is given a commission that some hope will destroy his career.

Tyger has recently mutinied, but instead of having her company dispersed around the fleet, as is customary, the ship is pressed into immediate service in the North Sea.

Kydd faces a crew still under some malign influence. Enemies aboard and on the high seas are just the start of the problem. Soon he will have to take his untested and untrustworthy crew into the Baltic, and there they will get entangled with Napoleon's invasion of Prussia.

The stakes are desperate, the task seemingly impossible, and the French implacable. But the only way for Kydd to avoid disgrace is to gamble his reputation and crew on a crazy mission to snatch a Prussian division out of the jaws of Napoleon's advancing army.

Will he return home once more a hero or himself face a court-martial?