Time Out of Joint

A mysterious Immortal is jumping through time. He's harvesting heads and causing incalculable damage to the web of time. Only Duncan MacLeod and his student Richie Ryan seem to notice the changes. As time warps around them they are unable to figure out how to stop it.
Trapped on their homeworld the Time Lords are powerless to intervene. In desperation, they disregard the first law of time and allow the first seven of The Doctor's incarnations to join forces to combat the threat and save all causality. If he can find a way.

Why does Duncan seem to recognize the Doctor's young companion, Ace? Will The Doctors find a way to combat the threat? What price will have to be paid to save creation?

A Doctor Who/Highlander Crossover.