In March 1815, on an icy road through the French Alps, Napoleon Bonaparte walked alone toward a battalion of royalist soldiers sent to arrest him, opened his gray overcoat, and invited them to shoot their emperor. They joined him instead. This episode follows the final stretch of his grip on power, from the quiet intelligence gathering on Elba to the mud of Belgium. It explains why the gamble looked possible: the restored Bourbons had humiliated the army’s veterans, and the victors at the Congress of Vienna were close to war with each other.

Napoleon slipped away with barely a thousand men and entered Paris on March 20 without a shot fired. Holding the throne proved harder. He recast himself as a constitutional monarch, yet a weary public barely voted and Europe declared him an outlaw. Facing nearly a million coalition troops, he struck north to split Wellington from the Prussians under Blucher. Illness, a brilliant British defense, and a lost Prussian army undid him at Waterloo, and within days his own parliament had turned against him.

• The Bourbons retired thousands of battle-hardened officers on half pay and replaced the imperial eagles with their own white flag, handing Napoleon a ready army.
• Marshal Ney promised Louis XVIII he would bring Napoleon back in an iron cage, then defected when his 6,000 troops made clear they would not fire.
• Liberal critic Benjamin Constant drafted a new constitution guaranteeing a free press, but only about 1.5 million people voted in the plebiscite.
• At Waterloo Napoleon could barely ride a horse, Wellington hid his infantry behind a ridge, and Marshal Grouchy’s 33,000 men lost track of the Prussians.
• He abdicated on June 22, surrendered to HMS Bellerophon on July 15, and was sent to Saint Helena, while France paid an indemnity of 700 million francs.