3. Louise Brealey
Why she should be next: So the companion needs to be someone who can deal with an abrasive, arrogant genius outsider who nevertheless has the best interests of the world at heart. This sounds like the part Louise Brealey has been playing on Sherlock for the past few years, so she has the experience to show shed be good in a similar role. Shes able to hold her own with fantastic actors such as the now-superstar Benedict Cumberbatch, so she wouldnt be overshadowed by Capaldis talent, and shes had good chemistry with a lot of her past co-stars too, which suggests shed be able to build a good rapport and an interesting relationship between the companion and the Doctor. Shes also got a good working relationship with both showrunner Steven Moffat and potential future showrunner and regular writer Mark Gatiss as a result of Sherlock. This means that shes used to bringing their scripts to life which should help her to hit the ground running. It also means that theyll be used to her strengths and weaknesses as an actor, so will be able to write a role that fits her to perfection accordingly. Why she shouldnt be: Despite the likes of Arthur Darvill saying theyd love to work with him again, Steven Moffat doesnt have a huge habit of re-using actors. Theres some crossover between the likes of Sherlock and Doctor Who, but no more than youd expect from two shows using the same limited talent pool. More intriguingly, neither show has had a guest performance from lead actors Moffat has used in the past, such as Jack Davenport and James Nesbitt, despite how often theyve been linked with the show. Matt Smith, too, was rumoured to have a role in a future Sherlock, but, as far as anything is known goes, that has thus far failed to materialise. All these would count against the chances of Brealey making the jump between shows. In addition, were Brealey to make the coveted leap to Doctor Who companion, it might make the show as a whole feel too similar to Sherlock, increasing the sense of repetitiveness between two shows that share the same writers. Since Doctor Who thrives on feeling refreshed and vibrant, making it appear similar to something that audiences have already seen a lot of might be something best avoided.