Politics makes strange bedfellows. In "Roosevelt and Stalin: Portrait of a Partnership," Susan Butler provides a rigorous study of one of the 20th century's unlikeliest alliances. Throughout her excellent book, Butler shows how the leaders of the capitalist and communist worlds had not a grudging marriage of convenience but a willing friendship, one founded on and motivated by a shared vision: to defeat Hitler and create a lasting postwar peace.

Butler begins with the Tehran Conference of 1943, where Roosevelt, Stalin and Churchill met to discuss the opening of a second front against Nazi Germany. It was here that Roosevelt also outlined his "get-tough concept" of a world government or "United Nations" led by "four policemen" — Britain, Russia, China and the United States. We hear how after Stalin finally cracks a smile Roosevelt feels comfortable enough to call him "Uncle Joe." A friendship is forged.

However, as Stalin and Churchill distrust each other from the outset, it comes down to "master manipulator" Roosevelt to mediate disputes, coax the British premier from his sulks and allay the Soviet tyrant's paranoia.

From here, Butler backtracks to the road to war, with Stalin deliberating over throwing in his lot with Hitler. After this, she takes us into the thick of war, with the German attack of Stalingrad and siege of Leningrad. The last part of the book is dedicated to the Yalta Conference of 1945, during which plans were drawn up to punish Germany and Japan. Here, as at Tehran, Butler takes us through each plenary session and meal, charting every move, countermove and stalemate. Her attention to detail should, by rights, slow the narrative's momentum, but, in fact, it keeps us gripped. An agitated Churchill lights one cigar after another; Stalin listens while "drawing numberless pictures of wolves, filling in the background with red pencil."

Butler's battle strategies and summaries are interesting, as is her chapter on Roosevelt's death, but it all feels like secondary drama. Far more prominent and thus far more revealing is the interplay between Roosevelt and Stalin — their commonalities, their differences and their feelings toward each other. A mutual respect shines through their exchanges. Roosevelt cajoles, convinces and reassures Stalin but never once kowtows to him. He manages to persuade him to re­instate religion in the Soviet Union. He is, we learn, the only person who "could speak truth to Stalin and have it permeate." When Roosevelt dies, a greatly shaken Stalin orders the Soviet nation into mourning — an unheard-of tribute for a bourgeois leader.

In her last book, "My Dear Mr. Stalin" (2006), Butler edited the complete correspondence between FDR and Stalin. In "Roosevelt and Stalin" it is not men of letters we see but men of action, men made real. The result is a rewarding read about a meeting of disparate minds.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Daily Beast. He lives in Edinburgh, Scotland.