Molly Zook was a bounty hunter based in Wyoming.
In 1899, she began following Clint Currie after a considerable bounty was put on his head. One night, she found Jata's crashed spaceship while riding through the desert. After getting closer to the ship, she discovered that the Twelfth Doctor was also there and offered to take him to a nearby town which Clint Currie's gang were going to attack.
After Currie's gang came into town, they pretended to go to the bank, because of this, the sheriff stationed all his men around it. Molly followed the Doctor as he swapped Jata with a regular horse and told the sheriff that Currie's gang were at the train station. After the Sheriff captured Currie, Molly collected the reward.