Little pic of David's parents. The other pics used in the article were old ones we've all seen a million times.
Pay attention, because this could get confusing. It's six days in the future. Christmas Day. About 6pm. You're wondering whether you should have another Ferrero Rocher, greedy pig: but pay attention, because Doctor Who is starting and it's David Tennant's second-last. Ever. The Doctor who made geekdom and specs and knowing stuff cool is about to die, and he knows it.
It's the past now. Sorry about this wibbly-wobbly, timey-wimey stuff, but this is Doctor Who. You'll cope. Russell T Davies, the man who runs the show, is starting to write that Christmas episode. He's sitting in his flat in Cardiff and he's wondering how to end the Doctor, end his run on the show - and, as a matter of fact, end time itself. He lights a cigarette (he's going to give them up in a few weeks, but he doesn't know it yet) and thinks: wouldn't it be brilliant to put Tennant with Wilf, the grandad of Catherine Tate's character Donna? Yeah, that'd be great. Wilf is 80 and the Doctor is 900 but they're the same, really: two old guys remembering, laughing, thinking about how things end.
Another time jump. Sorry. We're in the more recent past now. Just the other day, actually. But we've changed location. It's hot and bright and colourful. K9, I don't think we're in Cardiff anymore. It's LA, in fact, where Davies has been living for eight months, and he's telling me all about that moment in Wales when he started work on those final episodes. "I knew I was telling a story about the end of this Doctor's life," he says in that big-friendly-giant Swansean voice of his. "And I thought: how brilliant to put him with an old man. There's a sadness to it and a wisdom to it. When they talk to each other, the Doctor is more honest than we've ever seen him be with anyone else. He's in the unusual situation of knowing his death us on its way, and if anything is going to make you speculative about the past an who you are, it's that." Don't get too sad, though. This is Doctor Who, remember, and Davies says there'll be big monsters and big bangs too. There are two episodes in all: the Christmas Day one and another on New year's Day when Tennant's face will merge into Matt Smith's. It'll be sad for Tennant fans but it'll be sad for Davies as well - and certainly for the BBC. Although it was Christopher Eccleston who took Doctor Who back from the slightly-mocked nowhere to the top of the schedules, it was arguably Tennant who went on to give the programme its current ubiquity. Just like the heyday of Tom Baker in the mid to late 1970s, Doctor Who's face is now on books and toys and lunchboxes and pretty much everything else you can imagine.
Davies says it's all down to a brilliant central performance from Tennant. "My favourite thing about Tennant is that he's so light on his feet that you can write anything for him. I think the most marvellous thing about him is that, after four years on screen and a million repeats and all this iconography of the tenth Doctor all over the place, you still can't come up with one single adjective that describes him. We did that with all the past Doctors: we'd say the bohemiam Tom Baker, the loudmouth that was Colin Baker. You can't do that with David's Doctor - and he is one of the most studied Doctors in history. Yet he's kept it so elusive." Davies believes Tennant has also expanded the role; widened it. "You can take a serious scene and make it funny and you can take a funny scene and make it serious. He's so nimble. It's really significant that every year our audience went up, and not many programmes can say that." For Davies, writing all those episodes since the return of the show in 2005 has been about trying to find variation within a fairly fixed frame. "I remember coming to write the final episodes and thinking: shall I do a story - it's my final chance - where the Doctor becomes evil?" he says. "I know how brilliantly David would portray that. And then I thought no, I don't believe that story." Instead, with charactestic overstatement, Davies has gone not for the end of the world or even the end of the universe, but the end of time itself. There's an old baddie to fight - The Master, played with adolescent swagger by John Simm - and the Doctor's companion for both episodes is the aforementioned lively octogenarian Wilf, which is just brilliant in an industry that is so Botoxed and smooth. Wilf even gets to fire a laser gun. Can't wait.
OK, another time jump approaching. Are you getting used to it yet? It's a few weeks ago, and the man who plays Wilf, Bernard Cribbins - yes, the Bernard Cribbins - is telling me all about filming those episodes with David Tennant. This wasn't Cribbins's first Doctor Who, not by a long way: he starred with Peter Cushing in the 1966 movie Dalek Invasion of Earth: 2150AD. "I walked into the TARDIS and turned to David and said, 'The last time I was in here was 1966,' and David turned to me and said, 'I wasn't even born!'" That isn't Cribbins's only Doctor Who connection, either, because in a parallel universe he could have played the Doctor himself. He interviewed for the job in the 1970s but Tom Baker got it. "Ah, Tom Baker!" he says. "He used to be my favourite Doctor, but it's David now. And you know why? The eyes," he says. "The eyes." It's more than that, though. "One of the keys to David's success is intensity, which I like as an actor," says Cribbins. "He fixes you with those eyes and if you look at him in close-up you can see what he's thinking about. He's intelligent and intense and surprising, and that is essential. You've got to surprise the audience. Get them off balance. He likes to get smiles, too, though - and that is part of the writing. Russell gives you little changes that happen quickly. It's light but the moment of tension is still there. It's the youth of the man and the youth of the writing." The one thing Cribbins can't tell me is how the story actually ends, because even he hasn't seen the last four pages of the script - but, in another time-loop trickery, we can go back and find out how it started.
Tennant, who's 38, grew up in Paisley where his father, Sandy McDonald, was a minister. We're in a back garden there now. Mid-1970s. A wee boy's running about. Look. It's David Tennant. McDonald remembers the day. "From a little boy, as early as between three and four, his grandmother knitted a scarf for him and he ran about the garden being Doctor Who," he says. McDonals says he never remembers his son wanting to be a fireman or a doctor - not a real one, at least. "As I recall, David never wanted to be anything other than an actor," he says. "For many years, he thought he would never be Doctor Who, because it finished when he was growing up. I think he'd hoped he might have got it when Christopher Eccleston got it." McDonald has since got to see the making of Doctor Who up close - and was even in one episode, as a butler. "They were a very happy crew."
Shortly after Tennant landed the role he had wanted for so long, I went down to Cardiff in 2005 to meet the new man as he was filming his first episode. He's just seen the Cybermen for the first time that day and couldn't stop drumming his feet on the floor with excitement. He did admit to me, though, that - despite the thrill of it all - he'd had a couple of wobbles about whether to take the part. "Then I woke up one morning and thought, 'What are you farting about for?'"
On screen, Tennant has always played his Doctor with manic chumminess, but the actor himself is reticent, reluctant to unpeel his emotions. Mark Thomson, artistic director of the Lyceum Theatre in Edinburgh, who directed Tennant in Look Back in Anger, his last stage role before Who, says this shyness is not a problem. "With David, apart from maybe a traditional Scottish Calvanist reticence to be entirely open, his work is his work," says Thomson. "He's got an extraordinary life force and that shines on screen."
Playing the Doctor has lef to other juicy opportunites, but McDonald says it has also given his son a kind of benevolent power - a bit like the Doctor, really. Since the death of his mother, Helen, from cancer in 2007, Tennant has raised money for the Accord hospice in Paisley where she was treated. McDonald, who's 72, says his son was terrific during that illness. "He was very supportive of his mum and it meant an awful lot to her that she was able to see so much of what he was doing," he says.
When Tennant was away from the set and back in Scotland in 2007, he visited his alma mater, the Royal Scottish Academy of Music and Drama in Glasgow, for a Q&A session with students. Over the years, he has also taken part in the academy's mentoring scheme, which pairs up students with professionals. Hugh Hodgart, dean of drama at the academy, directed Tennant in a production of Tolstoy's The Fruits of Enlightenment when the future Who star was still at the college. "What was fabulous about him was he was off the book straight away," says Hugh. "I didn't have those thoughts at the time but then you think: 'That is such a huge part of what's got you where you are now, David.' He absolutely stood out." After Tennant left college, Hodgart offered him one of his earliest jobs, in Hay Fever at the Lyceum in Edinburgh.
One of Tennant's earliest bits of televison was Takin' Over the Asylum, a BBC drama about a radio station in a psychiatric hospital. It's 1994 now, by the way, and the actress Arabella Weir is also in the cast. She is introduced to this David Tennant guy and a few seconds later is doing a scene with him. I speak to Weir in London and she spins her mind back to that moment. "I'd only met him for a couple of seconds before we shot the scene and I remember thinking, 'Bloody hell, he's brilliant.'" she says. "I had a big house in London and he said, 'I'll come and be your lodger.' I was his landlady officially but we were much more like friends. In those days, I was more famous than him. People used to say to him, 'Oh, how do you know Arabella Weir?' And now I say, 'Ah, how the tables have turned!'" It's clearly not a problem for Weir, though: she's still close to Tennant, and her children, who are 10 and 11, are his godchildren. Their godfather is Doctor Who! How cool is that?
Cool. Interesting word. Doctor Who never used to be that, take my word for it. But it is now, kind of. With boys, girls, everyone. But Tennant's not universally popular. Time for another jump in time and place. It's a fornight ago: a pub in Glasgow. Outside it's wet and windy. The kind of day the TARDIS would land in. In a corner of the pub is a group of men, and three women. They are the Glasgow Doctor Who fan club, and they want to tell me what they think about David Tennant and what he's done for the show they love. "He's made the programme more modern," says Christine Blair, who's 48 and a classroom assistant. "I used to love Jon Pertwee but he was an old man and more of an authority figure. Tennant shows emotion that no other Doctor would have, and that's not a problem for me." Then John Hughs leans across the table. " I love him as an actor, yes - but as a Doctor, no," says John, who's 35. "He's popular with girls, and kids like him, but he's a little too manic for me. David's performance has brought in new fans but Christopher Eccleston was a better actor."
A short trip again, back out to Paisley, to meet Michael Coen, a writer and author of the Doctor Who short story Homework. Coen is a fan of Tennant and feels that, although Eccleston relaunched the show, Tennant was often more comfortable in it. "David has the ability to switch, often within a single scene, from a motor-mouthed science geek to the doom-laden - and scary - Last of Time Lords," he explains. "Few actors have that facility." Coen also believes this diversity will mean Tennant's post-Doctor Who career will surpass all other former stars of the show.
The signs are good already. Such is the time-twisting madness of Doctor Who and TV that, although his last episodes are still to be shown, David Tennant is already out there living his future, and has been for months. In fact, filming on his final Doctor Who wrapped last May and he is now in America making a pilot called Rex Is Not Your Lawyer, a comedy drama about a barrister who has panic attacks. He said that he'd had to audition for the role. "But that's good. You don't want to get complacent. It's not a tactical move. It's not like you sit at home thinking: 'Next year Hollywood!' There's no great plan. You just muddle along, and if an opportunity comes along, it would be silly not to take it."
Russell T Davies is out in Los Angeles too, of course, writing, thinking, dreaming. "I'm developing new stuff, nothing definite, just learning the way they do things here," he says. "Some stuff which is better than we do in Britain, some stuff which is worse. What I like about LA is that it's full of people obsessed with television. This town really makes sense to me." Davies will be trying to pitch scripts soon, and is a contemplative mood about where he's been, where he is and what kind of legacy his work on Doctor Who will leave. Time for our final jump, and it's a big one: more than 60 years in the future. "I know there are children now who will remember Doctor Who when they're 70 years old," says Davies. And that, he reckons, is the best possible legacy he could leave.