Fox spends most of this book on land, having been ordered to Acre to rendezvous with another ship and work with that captain. He never actually meets that ship but does find out that Napoleon has broken out of Egypt and is headed up the coast.
Why does this matter? As the book explains a couple of ways, if Napoleon isn't stopped here, he'll gather forces and followers and rampage his way to Constantinople and taking that he can head into Europe or, more troubling, go east into India where the British have wealthy holdings and need the cash to pay for the war. Fox does his part to harass and trouble the French, and then heads to Acre where he's met up with Miller, one of Nelson's Band of Brothers from the Nile who knows Fox.
Acre is in pretty sad state but soon, Fox and especially Sidney Smith the quirky, chaotic but brilliant sea Captain shore up the defenses and add cannons. Fox does his part to fight the enemy and the bulk of the story is a tense and bloody account of the siege of Acre, one of the lesser-known but critical events in the Napoleonic wars.
And, because its Fox, there are several twists, few of which go his way.