Part of the short lived Unbound series, this story asks "What if the Valeyard had won?" though I think a more accurate premise is what if after foiling his plans, the Doctor at the last minute decided to return to the matrix to save the Valeyard and the two ended up trapped locked in combat, what if the wrong person won that battle?

The most interesting part of the story is following the Valeyard as we get to see just how much chaos he would cause, a Doctor with no restraint untainted by conscience. For Michael Jayston's return to the role since Trial of a Time Lord, he really gives the Valeyard a chilling and demented edge, how he continuously taunts and threatens his companion and is willing to manipulate events of the past to get the outcome he desires. Mel's side of the story is to track down the Valeyard in the hopes of bringing the old Doctor back, or failing that killing him and she gets some badass moments. But unfortunately the ending is what derails the story for me, without going into spoilers, it uses a variation of "it was all a dream", which renders most of the story, including Mel's completely meaningless. It's still a harrowing ending that places our main characters in a hopeless situation, there was just a cleverer way to execute it than having the story mostly be an illusion.