In his first day as prime minister, Churchill immediately distinguishes himself from Chamberlain by appointing himself minister of defense and rapidly assembling a new government. He keeps Halifax as foreign secretary, gives Chamberlain a face-saving cabinet post, and delays moving into No. 10 so Chamberlain can leave with dignity. Churchill’s relentless style quickly transforms Whitehall: he dictates constant brief "minutes," demands precise language and short memoranda, works from bed or the bath as readily as from an office, and relies heavily on Major General Hastings Ismay, who becomes a key intermediary with the service chiefs. Ismay also sees how strongly ordinary Britons respond to Churchill, and Churchill is moved to tears by their trust because he believes he can offer only hard times ahead.

Churchill wants action as well as energy, and within two days RAF bombers strike a German city to show Britain, Hitler, and the United States that Britain intends to fight. On May 13 he gives his first Commons speech, promising victory while warning that he has only blood, toil, tears and sweat to offer. Meanwhile the military situation worsens sharply: Rotterdam is bombed, German armor smashes through Allied positions, and French prime minister Paul Reynaud urgently asks for more British fighter squadrons. On May 15 Reynaud telephones Churchill to say France has been defeated at Sedan, which shocks Churchill and pushes him to send Roosevelt a secret appeal for destroyers, aircraft, anti-aircraft weapons, and continued aid even after Britain can no longer pay. Roosevelt replies cautiously and offers sympathy, but not the immediate help Churchill wants.

Determined to see the crisis for himself, Churchill flies to Paris on May 16 with Ismay and other officials and finds the French position far worse than expected. French leaders again beg for aircraft, and Churchill, thinking of how history will judge Britain, promises ten squadrons. Back in Britain, fear of invasion rises and talk of appeasement resurfaces, provoking fury in the Churchill household: Clementine Churchill attacks David Margesson at lunch for his earlier support of appeasement, then later walks out of church over a defeatist sermon. After another alarming call from France, Churchill returns from Chartwell to London, learns the BEF may have to fall back toward Dunkirk, and decides Britain can no longer spare fighters for France because they are needed for home defense. In his first radio address on May 19, he warns that after the battle in France will come the battle for Britain, offering realism without admitting that withdrawal of the BEF is already under discussion.

The broadcast divides listeners, with some frightened and others strengthened, while the BEF continues retreating toward the coast. Churchill briefly sinks into depression over the danger to Britain and the empire, then, against advice, flies to Paris again in foul weather, though the trip achieves little. Because the strain is so great, the cabinet assigns Sir Charles Wilson as Churchill’s personal physician, but Churchill resists the arrangement and insists there is nothing wrong with him. John Colville, however, sees Churchill recover his spirits and grows increasingly impressed by his vitality, informality, and lack of self-consciousness even as disaster looms.

By May 24 the wider crisis is unmistakable. Halifax records his shock that the supposedly solid French army is collapsing with astonishing speed, and Churchill receives a chiefs of staff paper that avoids naming the unthinkable directly while nonetheless planning for it: a British strategy for the eventual defeat of France. The chapter closes with Churchill energized personally and politically, but facing the possible destruction of Britain’s position on the continent and the imminent threat of invasion.