A few days later Tito arrived and Maclean had to convey Churchill's displeasure at his sudden and unexplained departure. Tito had been to Moscow at Stalin's invitation, to arrange matters with the Soviet High Command. Maclean helped to hammer out a draft agreement, and went to London with it, while Tito's envoys took it to Moscow. "It was a difficult and thankless task. King Peter, quite naturally, was not easy to reassure, and Tito, sitting in Belgrade with all the cards in his hand, was not easy to satisfy." The bargaining went on for months, and meanwhile Maclean's staff wanted to get away, to assist guerrilla wars elsewhere. When the Big Three (Churchill, Roosevelt, and Stalin) met at Yalta in February 1945, and made it clear that Tito and Šubašić had to get on with it, King Peter gave in, and all the pieces fell into place. The regents were sworn in, as was the united government, and the British ambassador flew in. Maclean was finally able to leave.