In November 1943, with the outcome of the Second World War hanging in the balance, the Allies needed a new plan. The Americans' audacious suggestion to the Soviets was to open a second air front, with the US Air Force establishing bases in Soviet-controlled territory. Despite Stalin's obvious reservations about the presence of foreign troops in Russia, he was persuaded, and in early 1944 and Operation Baseball and then Frantic were initiated as B-17 Superfortresses were flown from bases in Italy to the Poltova region in today's Ukraine. Award-winning historian Serhii Plokhy tells the gripping, little-known story of this encounter between American and Soviet soldiers and how their collaboration quickly fell apart, mirroring the transition from the Grand Alliance to the Cold War. Soviet secret policemen watched over the Americans, shadowing their every move. A catastrophic air raid by the Germans revealed the limitations of Soviet air defences.