ghost, Will learns that his and Lyra's dæmons are now in the world where Lord Asriel is waging war on the Authority. They cut back there and escape with the dæmons to another world, narrowly avoiding the attentions of the Spectres they are now vulnerable to. However, when they wake up the next morning, the dæmons have fled from them. A group of highly developed animals approach them and carry them back to their village where Lyra's friend Mary Malone, a physicist from Will's world, is waiting among the Mulefa. They tell her about their adventures and in return Mary tells them about the time she first fell in love and how she stopped believing in God (she had previously been a nun). Will goes back out the next morning with Lyra to find their dæmons. When they stop to eat, Lyra feeds him a piece of fruit that was given to them by Mary (a reference to the Fall), and they realise that they have fallen in love with each other. Their love causes Dust, which is the source of human consciousness and free will, to stop escaping but instead to fall upon the world once more. However, the very next day their dæmons return and tell them what they have learned. To preserve the existence of Dust, all of the windows between the worlds must be closed, and because dæmons can only live for a short time outside of their own worlds, Will and Lyra must each return to their own world. Will is also told that using the Subtle Knife had produced the Spectres initially and that it must therefore be destroyed: he can no longer use it to travel between worlds. Will realises that he and Lyra must separate forever. Will, Lyra and Mary return to Cittàgazze and he cuts a window back into the Oxford of his world. Before they part, Lyra leads him to the University's Botanic Garden where she finds a certain bench, one that also exists in her world in the same place. They promise to return there, every year for the rest of their lives at noon on midsummer's day so they can feel close to one another again. Lyra steps back into Cittàgazze and Will seals the window behind her. Finally Will has to break the knife and he recalls how it had broken the first time, when he had