‘Girl in the Fireplace’ begins a trend in Moffat’s stories of exploring how travelling from one year to the next and back again affects the universes perception of the time traveller. Just as in ‘11th Hour’ the Doctor becomes a young girls imaginary friend and protector, there for her her entire life without aging a day.
Those who know the player characters, who encounter them several times during the years, will view them. They appear in times of trouble, rarely changing, and vanish until they are needed again.
This isn’t just confined to those who have immediate contact with the time travellers. People like Clive from ‘Rose’ can stumble across references to them and their actions throughout history.
What this means for the player characters is that they can quickly become legendary, appearing in myths and fairy tales told on hundreds of alien worlds. The further into the future they travel the more likely it will be that their reputation will have preceded them.
Time travellers become other worldly. They don’t age, they can be anywhere and everywhere. Even after they die people could still meet their earlier versions, still having adventures and defeating evil. In a way they become eternal.
You might want to avoid this. If taken to far then subtly goes out the window and challenge evaporates. If it reaches a stage where whole armies flee at the mere mention of the player characters names it will be hard to write an exciting adventure for them.
Instead think of them establishing their own mythos. They are now akin to figures such as Robin Hood, Zorro or Sherlock Holmes. People might associate certain items, clothes and forms of behaviour with the character, have an idea of who their friends and enemies are but the details might become confused and few would actually believe them to be real.
This mythic view of time travellers can lead to misinterpretation of the characters actions. Clive believed that the Doctor was a harbinger of death because where ever he appears so did trouble, confusing the cause and effect of events. This shows how people can take the same facts and read them in different ways.
From the player characters perspective everything changes so quickly that they only have to blink and it turns to dust. You can emphasise how people they encounter are aging, describe how even the buildings are redesigned or demolished and how the community is reshaped by events.
This is much more noticeable if the TARDIS keeps coming back to the same location, adventure after adventure. It can be interesting to craft a home base, such as the Powell Council Estate or the small village of Stockbridge from the Doctor Who comic, allowing you to craft a selection of supporting characters and describe how they and their surroundings are effected by the passage of time.
‘Girl in the fireplace’ avoids temporal confusion by making Reinette encounter the Doctor and his companions in sequence. This avoids the problem of referring to events in her past that forces the Doctor to travel back and ensure that encounter occurs.
Whenever a player character meets a NPC you will have to decide if you want to hint that there was a previous encounter. You might restrict it to a brief mention of ‘that business with the vampires in Hong Kong,’ as the Brigadier did in the Dr Who book ‘The Dying Days’ or you might hint at a whole history such as with River Song.
If you later wish to include an undisclosed prior adventure in that character past you could always have them sworn to secrecy not to mention it to the ‘earlier’ versions of the time travellers or the old cliché of amnesia making them forget this encounter.
There is a reason why they call it the ‘web of time’. Become to involved in a single place and time and you become stuck, bound by what you know occurred. As tempting as it might be to use the TARDIS to go back and avert everything bad that occurs to a beloved NPC they can’t because they didn’t, as much as they’d like to.
This is the reason that the Doctor gives to Mickey for why they can’t use the TARDIS during this adventure. It should also be discouraged during the course of most games. If they need a few more hours to stop the villain player characters might want to travel back in time but doing so brings its own problems.
Even if they were able to pilot it correctly, getting the right time and not finding themselves wondering for centuries in other eras, there would be a high chance of a paradox. They could run into their earlier selves, accidentally alter something that they know occurred or stop the villain to early, preventing their own trip back in time and wiping them out of existence.
There is a brief moment when Reinette gains some foreknowledge. Rose has just explained that sometime after her 37th birthday the clockwork drones will come for her when Reinette steps through one of the time windows on to the spaceship.
Through the corridors she hears the cries of the party goers, 5 years hence, on the night the robots attack. Among their voices she hears herself calling for the Doctor because it is time, the clock on the mantle piece has stopped.
Reinette now has an accurate piece of information to identify when the Doctor will come. At start of the episode we saw her looking at the clock and we understand now that it is the fact it is broken that tells her this is the night.
Foreknowledge takes into the realm of the mystic but uses science rather that the supernatural. It can be a powerful effect if the player characters know how to recognise the signs that something important is about to occur.
If they know that a king will be murdered by a man with a glass eye it will be on edge when they are introduced to just such a person at the king’s ball. Similarly if they have been told that an alien invasion began with a unseasonal snow storm the first flakes to fall will be that much more chilling.
They can gain this information from other time travellers, historical records gained from the future or a transmission sent into the past. What they do with this information and handle any resulting paradoxes, is up to them.
The reoccurring theme in the episode is that being a time traveller is a lonely life. Taking short cuts they watch people grow, age and inevitably die, sometimes in only a few hours of a time travellers life.
They have the choice of not making a connection or becoming invested and suffering loss for sake of the gain, just as Reinette will endure the monsters in return for the Doctor.