The Winter War was one of the side stories of the Second World War. In 1939, the Soviet Union decided to extend its defenses around Leningrad by taking out Finland, a former Russian province that had broken away during the Revolution. Tiny and poorly armed, war with Finland should have been short and victorious.

While the Finns lacked tanks, aircraft, and artillery, they had a deep reservoir of fighting spirit. The classic story is of Finnish ski guerrillas cutting road-bound Soviet columns to pieces in the frozen woods, and while that did happen, Trotter goes beyond the popular heroics to show the war as it really happened. These 'motti' tactics were ones of desperation and weakness. The Finns would have much preferred a quick victory so they could redeploy forces to the decisive theater of the Karelian Peninsula. On the Mannerhaim line, they held out through sheer will against uncoordinated Soviet attacks. Russian attacks were massive, but tanks and infantry didn't work together, and artillery alone couldn't dislodge the dug in Finns.

The Western powers promised aid, which was slow in coming and insufficient. Finally, in March the Soviets reorganized, and this time their attacks overwhelmed the Finnish defenders. Finland signed a harsh peace treaty at gunpoint, and then fought another hard war again as part of the Axis, the Continuation War. While Finnish casualties were small in absolute terms, and lopsided in relative terms, for a nation of 4 million people they were decimating, and the scorched earth defense, territorial concessions, and the later Continuation War left a bitter peace. The weakness of the Soviets may have played a role in Hitler's decision to betray his then ally in Operation Barbarossa, while also giving Stalin a hint of his military's failures, and enough time to initiate reforms that ultimately lead to victory in the broader war, though not without millions of dead Russians and other Soviet peoples in the process.

Trotter is biased towards the Finns, but not to the point of blindness. He admires their courage, but also notes that amateur tank hunting teams with satchel charges are no substitute for actual anti-tank weapons, which the Finns lacked. Their commander, Mannerhaim, was an archaic cipher, a Tsarist officer and Swedish noble who never mastered Finnish and who at minimum allowed atrocities when he was the leader of White forces during the 1919 Finnish Civil War, and may have ordered war crimes against Finnish socialists. But ultimately, he was the man of the hour, an iron-willed commander who enabled a stiff defense at a time other European powers collapsed. Trotter's book is about as good as an English history is going to get.