Quicksilver Captain is the story of Sir Home Popham (1762-1820), an extraordinary and under-appreciated personality of the French Revolutionary and Napoleonic Wars. Popham was a bundle of highly unusual contradictions. He achieved the rank of post-captain without a ship; he was more often employed by the War Department than by the Admiralty; and, as an expert in combined operations, he spent almost as much time serving on shore as at sea. In just over 25 years as a naval officer, Popham acted as an agent for transports, an unofficial diplomat, an intelligence officer, a Member of Parliament, an acclaimed hydrographer, a scientist and inventor, a publicist, and a government adviser, among many other roles.

Popham's career was literally as well as figuratively amphibious. So was his personality. Popham's well-known past as an illicit private trader, as well as his notorious lack of scruples, marred his reputation. People meeting him for the first time did not know what to make of him: 'He seems a pleasant man, but a dasher.' He fully understood the importance of communication and is best known for inventing a signal code that the Royal Navy used for decades. When he died, he left reams of correspondence behind him. But he also understood that words could either obfuscate or illuminate the truth, and his genius for twisting the facts to suit his own purposes made him an unreliable narrator. Many contemporaries distrusted and loathed him; after his court martial in 1807 for attacking Buenos Aires without orders (he escaped with a reprimand), many of his naval peers refused outright to serve with him again. And yet, even his greatest critics could not deny his abilities. One of his fellow naval captains wrote what could have been his epitaph: 'He is an extraordinary man, and would have been a great man, had he been honest.'

Quicksilver Captain paints a portrait of an ambitious man who built a career based on secrets and shadows. Popham's direct line to important patrons like William Pitt and Henry Dundas allowed him to play a role far beyond that of an ordinary post-captain. His ideas for using Britain's naval might for imperial defense and expanding British trade, as well as his knowledge of combined operations, made him the politicians' go-to expert. They wanted results, no matter what the cost, and Popham's willingness to play dirty - using bribery, threats, and experimental weaponry - appealed to them. In return, they protected him from his many foes, although in the end, they could not save him from his worst enemy - himself.