River's final instruction for Nardole was to save the Doctor from executing. Disguised as a , Nardole intervened in the proceedings and instructed him not to kill Missy as his late wife wouldn't approve. The pair were reunited with Bill when she arrived with the last survivors of the Ninth Legion escaping the creature. They travelled to a in the , where Nardole ran interference and sealed off the area of all but one of the Daleks. While he did not initially like humans, Nardole came to enjoy and , even knitting his own hats. When they arrived in , he expressed annoyance at the Doctor abandoning his oath again, but he followed the Doctor to investigate.
Appearing to accept that Bill and the Doctor were most likely dead, Nardole refuted the statement. They escaped after the Doctor distracted the Picts with popcorn. Knowing River would go to her in following their twenty-four years together on , the Doctor reassembled Nardole out of fear of being alone. He could do the , which rendered a victim unconscious in seconds. Following a battle with the onboard a , Nardole left the Doctor's company on his instructions to defend a small group of villagers.
Six months after the invasion began, Nardole visited Bill at her home and proved he was himself by answering questions about their adventures together. Nardole was a of the. On the , the body pulled Nardole's head out of storage to confirm River's identity before putting it back against his protests. When they travelled to a , he used it to short-circuit several panels and successfully quarantined all the Daleks in the vicinity to prevent them from attacking the Twelfth Doctor and Bill. Nardole presented Bill with the location of the Doctor, claiming to have recently found him. He did so, but not before the Doctor swore an oath to protect her body for a thousand years. He found a spaceship and used it to fly the Doctor, Bill and the Masters to safety when the Cybermen began to attack them.
Nardole initially opposed this but eventually relented, seeing his role as a babysitter a fitting way to make up for his past. In those two days, Nardole had his face painted to resemble the Picts and told stories outside the cairn. However, this could make him too ill to do anything for up to six weeks. However, Nardole accidentally found the and brought him to Professor Song instead. He also implied he could take control of the whole ship if he desired, but wouldn't as he had changed due to having met the Doctor. It was not long before it was revealed that the Monks were behind the pyramid's erection and, after displaying their powerful abilities of teleportation and telekinesis, the Monks revealed that they wished to rule the Earth but would only do so when they were asked as ruling the population would be easier if they went along with the Monks' plan.
She and Nardole arrived on Mars after the Doctor and Bill resolved a conflict involving and humans. Send me with them, I'll be selling their own spaceship back to them once a week. He watched with Bill and the Doctor as the Monks retreated from the Earth. Two days passed for him whilst the Doctor went in for a few seconds. When one of the soldiers fell back under the Monks influence, Nardole rendered him unconscious with a. He was particularly scared of heights. He appeared in all the Christmas specials from 2015 until 2017.
Nardole got the two onto the prison ship where he watched the confrontation between Bill and the Doctor. Escaping a former life of , which eventually made him an employee of , Nardole expressed deep for his actions and so attempted to make up for his illicit past. During this time, began to take a liking to him. Nardole remained behind on the ship with the Doctor's soldiers when he and Bill went to talk to Missy. He saw it as his duty to make sure the Doctor was alright following the death of River Song. Missy was placed in a and Nardole kept the Doctor to his word. Nardole, the Doctor and Missy remained at the top of the ship to incapacitate Jorj and eventually made their way down to rescue Bill, only for ten years to have passed for Bill, who had been converted to a Mondasian by.
The surgeon was required as River Song needed to extract the from the head of King Hydroflax. Upon their return, Bill admitted that Missy had stated that the best way to end the invasion was to fry Bill's mind. . He would later express for this period of his life. After the Doctor told Nardole they needed Missy's help, Nardole was shocked that they had gotten to that point. At the Doctor's oath, the pair would guard the vault for the next thousand years.
He was told to find. Although Nardole claimed to know very little of River's plans, there was only one way for Hydroflax's body to be sure, so it removed Nardole's head and attached it to its own. This was likely due to his cybernetic body. While stuck on , the Doctor took a job as a and Nardole acted as his. Nardole and the Doctor concocted a plan to test if Bill was still herself by setting up a scenario where the Doctor pretended to have converted to the Monks side. Nardole escaped with the Doctor, Bill and the remaining Picts after the Romans and chose to enter the portal to fight the remaining creatures.