Hot on the heels of the acclaimed third series, Doctor Who returns for a fourth instalment with a familiar face alongside the Doctor. Award-winning actor Catherine Tate returns as the Doctor's new companion, reprising her role as Donna Noble who featured in the 2006 Christmas special The Runaway Bride. Now reunited, the Doctor and Donna travel back to Pompeii in AD 79 on the eve of the infamous eruption where people are slowly turning to stone, investigate a series of grisly murders with the help of Agatha Christie, journey to the home world of the sinister Ood and come face to face an old enemy of the Doctor's. Series Four also sees the return of the Doctor's previous companions -- the vivacious Rose Tyler (Billie Piper) and the feisty Martha Jones (Freema Agyeman).