The David Tennant Treat 4 Today is a clip of David Tennant as the Tenth Doctor and Catherine Tate as Donna Noble from the Doctor Who Series Four episode The Fires Of Pompeii.
In this clip The Doctor and Donna, after arriving in Pompeii, discover a merchant sold the TARDIS to Caecilius.
The episode marks the first appearance of Peter Capaldi (later the Twelfth Doctor) in Doctor Who as Caecilius.
Apologies if this video does not play in your country.
