Board Thread:The Panopticon/@comment-25041817-20150105184924/@comment-86.26.222.62-20150123021420

All we know about what Kroton did is that the events of The Glorious Dead were undone. The Doctor even wonders aloud where Kroton put the Master. So maybe we can assume that he rewound time putting the Master back into the Eye of Harmony, thus setting up future appearances and his subsequent escape in Mastermind.