Back in 1973, I was one year old. "Doctor Who" was ten. For its anniversary, the powers that be decided that a multi-Doctor story was a great idea, and so "The Three Doctors" was born.
The story focuses on Gallifrey being attacked by some unknown force. The Time Lords, having exiled the Doctor to Earth a few years before, decide to get him involved, but come to the conclusion that just one of him won't be enough. So they send the Second Doctor to Earth to help the Third, while the First gets stuck in a negative space wedgie (this was caused by Hartnell not being in good health at the time), and has to help from a television screen inside the TARDIS. Soon the TARDIS, the Doctor(s), UNIT, Jo Grant and a game warden all find themselves in an alternate dimension where they find someone familiar to all Time Lords...
This is, without a doubt, the best of the multi-Doctor stories. It's not as bloated as "The Five Doctors" and not as weird and overly-long as "The Two Doctors". Plus Pertwee and Troughton are both at the height of their game and do a wonderful job bouncing off each other.
In addition to all the special features from the original release of this disc, you will also get, as reported by a reviewer on Amazon's UK site:
* 'Making-of' documentary
* When Doctor Who Was Uncool documentary
* Episode encoding/authoring errors on original release fixed
So not a tremendous amount of stuff, but still good.
This is a great story, and a great recommendation for any fans of the series.