The Incubus (S01E09)

Bulstrode scours London in search of Robert, unaware that Robert has escaped to the countryside and is hiding at the Jezequiel house with Ravi and Olalla. To his astonishment, they are soon joined by Lily, who insists she figured out Robert's hiding place. However, Ravi starts to have doubts, suspecting that the entity they believe to be their friend is actually a shape-shifting creature called an Incubus. As the others succumb to the creature's influence, it becomes clear that this monster might have the power to bring Lord Trash back to life.