Grayla briefly travelled with the Tenth Doctor.
Grayla was a Gråttite, born on the planet Grått. She grew up hearing stories of the Mörkön and how it would terrorise the planet if they showed any emotion. However, she was a vibrant and passionate person and Grayla grew bored of the planet and travelled to the stars.
Upon her return, Grayla wished to change things. She told some of the younger Gråttites of the things that the Doctor had showed her and that they shouldn't hide their emotions all the time. This caused many Gråttites to believe that the Mörkön was a myth invented to scare children.
Many people visited the Whispering Gallery and began to mourn their loved ones. The grief awoke the Mörkön and caused him to kill all in its path. The monster had been trying to find Grayla, whose intense emotions acted like a beacon. Grayla refused to leave the planet. She was tranquillised and kept emotionally numb until her death, allowing the Mörkön to return to its slumber. Her last thought was held in the Whispering Gallery and was a message to the Doctor: "Doctor, they were right, they were right all along. This is no place for emotion. When you come, you must remember that."
When the Doctor visited Grått, his grief over Grayla's death awoke the Mörkön once again; however, his wealth of positive and negative emotions overwhelmed and destroyed it. He revealed to the people of Grått that Grayla would have been able to do the same thing, had they not sedated her.