Since ‘A Good Man Goes To War’ Madam Vastra has been portrayed as one of the Doctors closest allies. She is still a Silurian, first encountered by the Doctor slaughtering tunnel workers and commuters.
Although married to her human, Jenny, Vastra still eats humans. So far they’ve all been criminals (Jack the Ripper and a child poisoner) but she is still deciding to take the law into her own hand, not only killing sentient beings but eating them as well.
No matter how well meaning her intentions Vastra is a murderer. Not only that but Jenny, Clara, Strax and the Doctor are all complicit in her actions. They seem untroubled by her behaviour.
Previous incarnations of the Doctor have frowned on using violence and particularly murder. The 3rd Doctor constantly tried to persuade the Brigadier to avoid violent confrontation, 4th Doctor disapproved of Leela’s Janus thorns, 10th Doctor claimed he was the man who never would. In ‘Deep Breath’ the 12th Doctor knows he will probably have to kill the Half Face man but doesn’t relish the thought.
There have certainly been times in which the Doctor has killed but it is not something he sets out to do. Jenny makes it clear to Clara that Vastra will be eating the child poisoner after she is finished questioning him. They are both at ease with the situation.
We might suppose that it was the 11th Doctor who became friends with Vastra. That incarnation wrestled with the ethics of killing. That in letting your opponents live you are indirectly responsible for whatever pain and suffering they cause later. We see this especially in ‘A Town Called Mercy’.
Other incarnations of the Doctor might not find it so easy to tolerate the actions of Vastra. It is easy to imagine an adventure in which an earlier incarnation of the Doctor and his companions stumble across a Silurian and Sontaran working together with the aide of their maid to kill and eat criminals. The 3rd Doctor would be particularly suited for this.
You can rationalise this as how Madam Vastra always ended her career as a detective. When the 11th Doctor found her he realised how she’d come to be a detective in Victorian London and simply ensured that she fulfilled her destiny, all the while knowing his earlier self would defeat her.
There could be other consequences for Vastra’s actions. What if she were to act as judge and executioner on a suspected criminal only to find evidence that proved his innocence after she’d eaten him?
While Strax might not have a problem with this Jenny might. It would call into question everything they’ve been doing. It could be that Vastra isn’t that great a detective and has been ignoring the facts simply so that she can justify eating the human meat she hungers for.
Would Vastra stop if asked? Would her cravings cause her to turn on Jenny? We’ve seen her become more animalistic in ‘The Name Of The Doctor’ (when time was being rewritten) but we might see this happen again.
Inspector Gregson is shown to be a bit of a joke but what if a more competent member of the police worked with Vastra? He might object to her devouring of suspects or the knowledge could be made public.
Vastra could find herself under arrest and the courts would be unlikely to go easy on someone whose ‘disfigurement’ make her appear to be a monster. If Vastra defended herself she could make the situation worse but she’d likely face the death penalty for her crimes.
Jenny and Strax might turn to the Doctor for help (if they can reach him) but would he? They could try to rescue Vastra but if they succeeded they’d be wanted criminals, forced to go on the run.
If through some miracle they avoided detection there is also the question of their future. We don’t know how long Silurians live but there is a good chance Vastra will outlive Jenny. How would she cope without a human she’d considered a friend? Might she once again think of them as monkeys and decide that it was okay to eat who she pleased?
This could lead to a UNIT or Torchwood adventure. By the ‘modern’ day Vastra has lost much of her humanity, dwelling on her memories of her lost love and past triumphs while sating her hunger.
To the PCs she might appear as nothing more than a monster. If they learn of her good deeds will that change the fact she has eaten so many people and likely to kill again in the future? The choice for UNIT might be simple, while a Torchwood team might recruit her (if for nothing more than to keep an eye on her.)
This raises the question of whether PCs are allowed to murder in your own campaigns. This can seriously affect the tone of your games and also influence the decisions that they make.
For a harmonious game the GM and the players should come to a decision. This can lead to discussion about when it is and isn’t okay for them to kill the bad guys. When do they give them a chance to surrender and when do they take their lives?
This can be influence by the era and framework of your campaign. Mercy and justice could be important to your Time Lord PC and his campaigns while a group of UNIT soldiers will do what must be done to protect the world.
If your group enjoy drama not all of the PCs have to agree on the same approach. Some might want to capture their enemies so they can face justice while others might want to eliminate the threat forever. Both sides should have chance to argue their case and the ramifications of their decisions should play out throughout the campaign.