Not everyone who wants to travel with the Doctor gets that chance. Such is the fate of Journey Blue, who is turned down by the Doctor at the end of ‘Into the Dalek’. The reason he gives is that she is a soldier but what does this mean?
It could be that he disapproves of the profession. Certainly he has opposed military action, even while working with UNIT. Yet as late as his 11th incarnation the Doctor considered the Brigadier a dear friend.
Journey Blue also didn’t choose to be a soldier. She is a rebel, suggesting that she lived in a Dalek controlled sector and was fighting for the freedom of her race. It was either that or live in subjection. It would be cruel (even for the 12th Doctor) to discriminate against her on that basis.
Rather it might be that the Doctor is often deeply affected by his companions. Frequently they are the ones who motivate him or give him direction. In recent years both Amy and Clara have been vital to allow the Doctor to see what he missed.
His rejection of Journey Blue could be because of the point of view she’d bring. Her militaristic state of mind might only see violent solutions to the problems that they face. Combat could be the only way of life she knew and that would affect how the Doctor dealt with challenges.
There is plenty of evidence to suggest that the Doctor already has trouble finding peaceful solutions now. He has lived through so much war and death that the first solution that occurs to him are already those that involve death.
The 12th Doctor knew that he’d need someone with a different point of view. Someone who could argue with him. Someone who wasn’t afraid to defy him in order to force him to reconsider. Which brings us to the other issue with a soldier. Journey Blue could be so used to following orders that she’d do whatever the Doctor wanted without question.
This is not always a good thing. The Doctor can be pragmatic without considering the impact on others. In social situations he can be rude and in other situations he can be ruthless. His companions need to be able to point out when he has crossed a line.
The Doctor might also have promised himself that he wouldn’t take a soldier as companion. We know from ‘A Good Man Goes To War’ that he has many rules to keep himself in check. Having a soldier with him could be too much of a temptation.
In ‘Journey’s End’ Davros taunted the Doctor, pointing out how he’d turned his companions into soldiers to fight for him. Although this deeply affected him it was behaviour he continued, assembling warriors to fight alongside him in ‘A Good Man Goes To War’.
If he had one soldier as a companion how long before others joined her? How long until the Doctor carried his own army within the TARDIS? It would be a path he’d have trouble turning from.
‘Into The Dalek’ repeatedly explored the notion of self-sacrifice, with others dying for the Doctor. If Journey Blue joined him he would know that she’d be willing to sacrifice herself if he convinced her that it was necessary. His rejection could be based on his unwillingness to have that on his conscience.
In ‘The God Complex’ the Doctor talks about how he knows he is being irresponsible taking people with him. That he knows that it could end in their deaths and really his offer to travel with him is no choice at all.
Fate often plays a part in who he chooses to travel with. They either push themselves on him (Ian, Barbara, Ben, Polly, Leela, etc) or be stranded or lost and need his help (Vicki, Steve Taylor, Nyssa, Ace, etc). Sometimes taking a companion would be part of solving a larger puzzle (for example Amy and Clara).
In those occasions the Doctor could ease his conscience. Either he had no choice or the choice was left to the companion. It is quite different if someone asks him if they can join him. If he says yes and they die then their deaths are directly tied to his decision. This might be the same reason that the 4th Doctor refuses Leela’s request to travel with him. Asking to join him will almost always lead to rejection.
There could also be the impact on history should the companion join them. We can assume that Clara will have little impact on the grand scale of things. In a relatively stable period of history her influence is restricted to the students at Coal Hill school.
A soldier is a different matter. The loss of Journey Blue could mean that she doesn’t help the rebels secure vital victories against the Daleks. Without her presence they could be wiped out and humans might forever be the slaves of the Daleks. The 12th Doctor’s comments could be mean that because she is a soldier she is too valuable to take with him.
At this point in the 12th Doctor’s life he appears to enjoy having time to his self. In both ‘Deep Breath’ and ‘Into The Dalek’ the Doctor leaves Clara for a long time while ‘distracted’. Having a companion with him full time might prevent this.
These points can be useful in determining how PCs can join Time Lords (especially the Doctor). If they are soldier how can they overcome objections to secure their place as part of the TARDIS crew?
You can also explore scenarios in which Journey Blue does join the Doctor. She has a tragic background (with the loss of at least her brother), useful skills and lots of potential. Throughout ‘Into The Dalek’ she is learning from experience and Clara what it is like to work alongside the Doctor. She is certainly prepared for the role.
Would things have turned out as badly as the Doctor thought? How might she change and develop through their adventures together? If she travels with the Doctor full time would he forget about Clara? Would Clara be okay with this or get jealous? What if the Doctor turned up alone for their next adventure and refused to explain what had happened to the missing Journey Blue?