Epilogue.
Five years later in Oakwood, after the Doctor and Jessie had left, time went wrong. Every event from when the Doctor and Jessie had met until when they had left, repeated. So when the double of the Doctor and Jessie left, it meant that they could be anywhere. So the two times could cross, the real Doctor and Jessie and the double of them, some time in the universe. And if time crossed…all of them would die…
And it was all down to the mirrors. The windows hadn't closed to whoever made them and Jessie was connected. Because when she was four she had looked into a mirror and something was now watching her…repeating everything she did with the Doctor…risking her life so one day…the Doctor and Jessie would die…