Chantal is a scientist and an expert in manipulating biological matter from some time in the distant future, after the Great Retrenchment of 436,000 at this time, there was a massive space battle in Monoceros between Kallix Grover and the Sine Wave Shrine of Shillitar (Nothing was ever revealed about why these two races/governments/whatever were at war in the first place), which resulted in Earth being caught in the crossfire when a massive reef of magnetic energy missed its target and drifted billions of miles off course at about a million times the speed of light, smacking into Earth and wiping every computer on the planet. The state of technology was such that there was a computer in everything, and the vast grid of nanotechnology curled up and died in under a second, resulting in fire, plague, famine, and war, as well as the planet being cut off from its colonies.
The after-effects of this catastrophic destruction meant that humanity turned to analogue technologies during its ten thousand year Dark Age, their major technologies being biology and chemistry as they became able to do anything they want to the body, including the brain. Humans from this era had mapped out their anatomy so precisely that they could easily take a human body apart and put it back together with no ill effects, and manipulate the body to the extent that not only did pregnancies last less than a week, but even men could give birth. However, there was one particularly horrifying aspect to this future, most people from this era, apart from a small group called the Refusers who believed that raw human emotions enabled them to savour life, use chemical blockers – small devices strapped to their bodies – to regulate their emotions by tapping a few buttons, and, a result, nobody ever feels anxious or worried, and nobody ever strived for anything other than what they already had. Essentially, the human race had become a team of superhumans as emotionless as the Cybermen, lacking only the mechanical components to be identical to the former Mondasians.
One of the great geniuses of this era was a woman called Chantal, who possessed an elevated intellect of plus-810, and had been an expert at genetic engineering since she recreated her cat when she was twelve to ‘make it better’. Unfortunately, her desire to ‘improve’ life was such that she eventually decided to try and ‘improve’ the human race itself, concluding that homo sapiens was perfectly adapted for survival as primitive hunters in a cold climate, but after the Ice Age, the hard-wired aggression and competitive nature caused them to spread across Earth like a plagueat this point, the surviving humans had acquired a ‘rip engine’ – a dangerously primitive time machine that was outlawed by any civilisation that survived its discovery – and were intending to use it to travel back in time to observe the dawn of human history. Killing off her rivals (Having eliminated her empathy with other human beings to ensure her plan wouldn’t be hampered by pangs of conscience), Chantal took charge of the project and travelled back in time, secretly breeding an ‘upgraded’ form of humanity called the Hy-Bractors, using the extra energy from the rip engine to accelerate their growth while sending other members of the expedition to be eaten by the Hy-Bractors. Once they had achieved full strength, Chantal intended to unleash them on Earth, leaving them to devour all humanity and create a Utopia in her image.
Fortunately, her use of the rip engine to send a troublesome caveman into the 21st century attracted the Ninth Doctor’s attention, due to the energy released by the rip engine. While Captain Jack Harkness stayed behind to educate the caveman in how to exist on Earth in the present (The rip engine having altered his physiology to such an extent that he couldn’t go back to his own time in the TARDIS. without being torn apart by the time vortex), The Doctor and Rose Tyler travelled back to prehistoric times to find out what the rip engine was doing there in the first place. Once there, The Doctor and Rose befriended a Refuser called Quilley – the only person there who exhibited any actual curiosity about their presence – and discovered the truth about the Hy-Bractors. Unfortunately, The Doctor and Quilley were subsequently captured by Chantal as they confronted the Hy-Bractors, and Rose, while exploring the outside world, was ‘rescued’ from a group of neanderthals by a primitive human tribe
With The Doctor captured, Chantal drugged him up with various chemicals while she cut his body up and examined it before stitching him back together, The Doctor’s brain being so addled that he willingly told her about the Time War and the TARDIS. Luckily, his alien biology allowed him to fight off the drugs long enough to come up with the ‘plan’ of overpowering Chantal and escaping to look for Rose Quilley. With the Hy-Bractors unleashed – Chantal having accelerated her plans due to The Doctor’s interference – Rose and The Doctor managed to convince the primitives to retreat, but they were subsequently captured by Chantal… who removed Rose’s head (Albeit leaving her conscious and able to control her body) and threatened to leave it that way unless The Doctor agreed to cooperate and give her access to the TARDIS. Using Rose’s continued control over her body, The Doctor managed to distract Chantal long enough to slam a ‘combo pack’ of chemicals onto her, programming in a sequence that left Chantal totally unconcerned about The Doctor’s victory.
Using the equipment in the laboratory, The Doctor managed to force-cultivate a specific gene and splice it into gut bacteria, subsequently dispersing the concoction through the air. As a result, all the humans in the vicinity temporarily acquired the ability to breathe fire, using it to destroy the attacking Hy-Bractors. Only vaguely aware that her plans had been thwarted, Chantal attempted to use the rip engine to travel to the 21st century, but it subsequently tore her apart after she activated the machine. After Rose’s head had been reattached, The Doctor and Rose departed in the TARDIS, leaving the surviving members of the expedition to make new, natural lives for themselves with the primitive humans of that time.