Doctor Who: The Bells of Saint John, spoiler-free preview The Time Lord makes his return after the Christmas episode, and finally we get to see the proper introduction of his new assistant - Clara Oswald (Jenna-Louise Coleman). We've already met her twice, of course. And she's also died twice. But this being the Whoniverse, we should have known that such a little thing would not hold her back. Much like in the Christmas episode, we're back in London, but now the action takes pace in our own, internet-driven age. Perhaps Moffat - who wrote this episode himself - has been enjoying Charlie Brooker's Black Mirror, as there's a similar theme of the possibilities of evils within technology. Most exciting is the gleeful use of central London's landmarks by the Doctor and his fast-talking new assistant, who speed around the city in a bid to battle the malevolence lurking in the Wi-Fi. In all, Moffat has penned a witty nail-biter, liberally sprinkled with clever, modern ideas - and naturally a lot more happens than I've revealed here. We're also promised big things in future episodes, including a visit to Ancient Egypt, a submarine, Diana Rigg, deeper exploration of the Tardis, the return of the Cybermen, more episodes written by Mark Gatiss and Neil Gaiman and the 50th anniversary episode. Most intriguingly of all, Moffat has declared that "The Doctor's big secret will be revealed." Doctor Who returns on Easter Sunday