The Doctor soon realises the trap they have fallen into, and helps to save Rose, the Queen, and Sir Robert from Father Angelo's men and the werewolf by taking shelter in the estate's library, its wood coated with oil of mistletoe wood to stave off the beast. They study the library and discover evidence collected by Sir Robert's father, a polymath, and Prince Albert which indicates the werewolf is really the current form of an alien species that survives by passing its lycanthropic form from human to human. The Doctor also realises that the estate was designed as a trap for the werewolf, as by use of its strange telescope along with the Queen's Koh-i-Noor diamond, its cut fashioned by Prince Albert, they can destroy the alien lifeform.