It's official: Bionic Woman star Michelle Ryan co-stars in Doctor Who's Easter special, "Planet Of The Dead." And she's already begun her journey with David Tennant. Click through for tons of pics, with minor spoilers.

According to the BBC, Ryan is playing Lady Christina de Souza, "a woman with a mysterious past who's going to have a huge impact on the Doctor." Her one-off appearance doesn't mean she can't return in 2010 as a regular companion, since Donna Noble already achieved a similar feat. (And those of you who saw Ryan's cringe-making Bionic performance should bear in mind, she's a better actor when she doesn't have to fake an American accent.)

Last night, fans observed the filming of a scene where Tennant and Ryan were riding the bus to Victoria. Also, there was a scene of Ryan in an alleyway, where she burst from a doorway and ran into a crowded city street. And policemen seemed to be arresting a businessman in a pink shirt.

Meanwhile, comedian Lee Evans will play Malcolm, "whose life becomes connected to the Doctor's in unusual circumstances." [BBC and Doctor Who Forum]

Images by WENN, except for top image by BBC.

Send an email to Charlie Jane Anders, the author of this post, at charliejane@io9.com.