The Doctor is played by comic actress Arabella Weir--who would go on to appear in a small role in the 2011 Christmas special "The Doctor, the Widow, and the Wardrobe". She does a decent enough job as the Doctor--this is basically a "What If" style story set after the events of the Second Doctor story The War Games. Instead of the Second Doctor being forcibly regenerated by the council of the Time Lords, the Doctor escapes and commits suicide which, we're told, always results in a Time Lord changing sex upon regenerating. I'm not sure what to make of that, if anything. She hides out on Earth and falls into a life of heavy drinking at a local pub with two co-workers from a job she takes at a local supermarket. David Tennant and Toby Longworth play two Time Lord councilmen sent to Earth to track the Doctor down and bring her back to stand trial.
Most of the jokes fall flat but Weir and Tennant manage to make a few work just from sheer skill as performers. My favourite bit is where the Toby Longworth Time Lord tries to lay a trap for the Doctor by interrupting a television transmission with footage of himself wearing a rubber mask pretending to be an alien threatening Earth--a reference to a television signal hijacking during an American Doctor Who broadcast in the 80s where an unidentified person dressed as Max Headroom interrupted a broadcast of Horror of Fang Rock. Tennant's reaction to Longworth explaining the plan is pretty funny as he notes what a long shot the plan is, how unlikely it is for the Doctor to happen to be tuning in at that particular time.
Tennant played minor roles in several Doctor Who audio plays before he became the Doctor himself--I first heard him playing a Nazi guard earlier this week in the 2001 Seventh Doctor story Colditz in which the Doctor and Ace visit Colditz Castle when it was being used as a Nazi prison for enemy combatants during World War II. Written by Steven Lyons, it's the first Seventh Doctor audio I've heard that really capitalises on the Seventh's established personality as a master game player. The story involves the effects of an alternate timeline manifesting in the current one in what turns out to be an almost Moffat-ianly complex way. It's a good listen--Sylvester McCoy and Sophie Aldred turn in good performances as usual and the story advances Ace's personal storyline a little more, the one that was cut short by the series cancellation in 1989.