As the 10th incarnation of the time-travelling Doctor Who, actor David Tennant tackles daleks and cybermen in a manner best described as cocky. Sitting in his trailer at 3am, however, as the wet, miserable Cardiff night whips into a frenzy outside, he's considerably more reserved. He even admits there are times when he's still consumed by self-doubt.

"You always strive to know you're doing it right but I think the day you imagine you're getting it right is the day you should leave almost immediately," he says, in his trademark Scottish accent. "I had many a wobble and still do."

His biggest wobble, he says, was just before his debut episode, The Christmas Invasion, which screened in Britain in 2005. "The show had been such a huge hit. It was such a big deal. So much had been written and speculated on and I guess it was the thought of people saying, 'Oh, he wasn't as good as the last chap,"' he says.

His fears were misplaced. In fact, Tennant is now considered by many to be the best Doctor since the iconic Tom Baker.

Tennant returns for a second season (the revamped show's third) this week - first in the Christmas-themed special The Runaway Bride, then in the first regular episode of the series, Smith and Jones, which introduces his new companion, student doctor Martha Jones (Freema Agyeman), who replaces Billie Piper's Rose Tyler.

"We had three months off, and one week back it feels like you've not gone away," Tennant says, laughing. "Billie is not here this time so that's very different. That was the status quo I came into and in a sense that's now reversed. I'm now the status quo that Freema's going to have to get used to. But it's going great guns."

The schedule, he says, is relentless. The show's svengali, writer-producer Russell T. Davies, is a notoriously tough taskmasker. "As long as you keep a little ahead of the schedule, it's an easy rhythm to be in," Tennant says. "If you let it creep up on you, then suddenly you're having to memorise a lot of scientific bafflegab five seconds before you go on set. I'm quite good at keeping in front of it."

In the Doctor Who tradition, which began in 1963, the Doctor travels with a companion - typically a headstrong girl with an inquisitive mind and a screaming voice. Piper's Rose shifted the normally subsidiary role of companion into a leading part, which puts enormous pressure on Agyeman.

At the same time, cast renewal provides scope for change. "It allows the characters to develop, which is always the trick with a long-running series," Tennant says. "You want the characters to stay essentially the same but at the same time to make it interesting and, from an acting point of view, to keep it interesting. It's about finding where they go next and although the basic premise remains the same, it's how they move on through that."

The Runaway Bride is lighter in tone than many episodes, although Tennant attributes that perception to the prominence of guest star Catherine Tate, an actress largely known for her work as a comedian. She plays Donna Noble, who is abducted from her wedding by an alien energy source and deposited in the Tardis.

"Catherine is an actor first and foremost and she is very funny and the character is very funny at times, but it's still essentially dramatic," he says. "Hopefully the idea is that it will be something very exciting, very taut and quite a caper as well."

Each season of the revamped Doctor Who has had a story thread culminating in the final episode - first "bad wolf", which turned out to be a clue sent back through time and space by Rose during her confrontation with the daleks, then Torchwood, the secret organisation featured in the spin-off series Torchwood.

This year it surrounds recurring references to a "Mr Saxon", who is, internet scuttlebutt suggests, the identity of the Doctor's greatest enemy, the rival Time Lord known as The Master. Tennant is giving little away. "There is an exciting story running through it which will take the Doctor somewhere else and by the end of the season he will have had a real journey, both physically and emotionally."

Doctor Who: The Runaway Bride airs on the ABC on Thursday at 8.35pm.
The new season begins on Saturday at 7.30pm.

Source: The Sydney Morning Herald