Doctor Who takes on flesh-eating bugs and the Almighty

It has already revived the Daleks and carried a clear anti-war message. Now the writers of BBC's hit revival of sci-fi classic Doctor Who plan to mix current affairs and television nostalgia with plotlines inspired by subjects ranging from the MRSA epidemic to Hammer Horror films.

The second series of Doctor Who, starting on BBC1 on Easter Saturday, takes the time lord to places he has never been. For the first time, the Doctor, played by David Tennant, falls in love and ponders God's existence.

In a further break from tradition, the chief scriptwriter Russell T Davies said he "wouldn't think twice" about casting a woman in the lead role when the Doctor next regenerates, adding that he would love Sigourney Weaver, star of the Alien film trilogy, to appear.

The opening episode takes place on "New Earth" in New New York (actually the Gower peninsula). There, a race of nun-like catwomen run a hospital with a dirty secret. Hidden in the basement are thousands of humans infected with every known disease. Davies said that when he was writing the episode: "Everyday, MRSA was in the newspapers."

There are also parallels between the storyline and the debate over animal testing. "That's the way I write. I can't help it. I'm not saying I'm against animal testing," said Davies.

From contemporary to historical, the second episode features a fictional Queen Victoria, who is waylaid by a werewolf on her way to Balmoral. "It's very British - that Oliver Reed, Hammer Horror thing," said Mr Davies.

In other episodes, the Doctor and his assistant Rose Tyler, played by Billie Piper, encounter the Devil, a squid-like monster and winged Gremlins. Old Doctor Who favourites such as the Cybermen and the robot dog K9 also make a comeback.

The first series of the revived Doctor Who drew more than 10m viewers on Saturday nights, and a star-studded cast has been signed up for the second, including the comedian Peter Kay, who wrote a letter to Davies asking for a part, Zoe Wanamaker and Shirley Henderson. Stephen Fry is writing for the third series.

Piper refused to comment on speculation she is planning to leave the show. But insiders said she was likely to leave early in the third series. She was upset not to have been nominated for a Bafta.

"I was hoping to be there... because I love the Baftas. I would be lying if I said it didn't mean anything... but I'm 23 and I've got the rest of my life to do it," she said.

Tennant said he was enjoying the freedom that the role of the Doctor allows.

"One of the things with the Doctor is you're not obliged to take a character that already exists. It's not like James Bond or Tarzan or Sherlock Holmes. Part of the point of the whole regeneration thing is you've got a blank canvas," he said.