Acclaimed actress Lindsay Duncan will guest star in the second Doctor Who special of 2009 on BBC One.

Lindsay is best known for her roles across stage and screen, including Shooting The Past and GBH and is soon to star as Margaret Thatcher in the highly anticipated BBC Two drama, Margaret.

In Doctor Who she will play Adelaide – the Doctor's cleverest and most strong-minded companion yet.

Lindsay commented: "I'm thrilled to be involved in Doctor Who. I've never done anything like this before and I'm really looking forward to working with David Tennant and the Doctor Who team."

Lindsay joins David Tennant as he continues his role as The Doctor in the second instalment of the four Doctor Who Specials to be screened throughout 2009, which will follow Planet Of The Dead, due to air this Easter on BBC One.

Executive Producer and writer Russell T Davies said: "Lindsay is an incredibly talented actress and I've been an admirer of her work for some time. We are delighted to announce that she will be joining the team and playing the Doctor's most strong-minded companion yet."

The second episode is written by Russell T Davies and Phil Ford.

It is due to go into production in Spring 2009 and will be screened on BBC One later this year.

The Producer is Nikki Wilson; Executive Producers are Julie Gardner and Russell T Davies.

Mars, 2059. Bowie Base One. Last recorded message: "Don't drink the water. Don't even touch it. Not one drop."

Doctor Who will return to BBC One on Sunday 15 November for The Waters Of Mars – the second of four specials airing throughout 2009.

Starring David Tennant as The Doctor and guest starring acclaimed British actress Lindsay Duncan – best known for her roles across stage and screen (Margaret, Rome) – The Waters Of Mars is set to be one of the most scary episodes of the series to date, as a creeping infection beneath the Martian surface threatens not only the human race, but also the Doctor's most fundamental beliefs – with terrifying results.

Lindsay Duncan stars as Adelaide – the Doctor's cleverest and most strong-minded companion yet.

Neighbours, Flying Doctors and Casualty star Peter O'Brien also guest stars as Ed, Adelaide's second-in-command at the base.

The Waters Of Mars is the second of four specials which will air throughout 2009.

The Waters Of Mars is written by Russell T Davies and Phil Ford and is directed by Graeme Harper. The producer is Nikki Wilson.

Doctor Who: The Waters Of Mars, Sunday 15 November 2009, 7.00pm, BBC One