Will is eighteen when he figures out how to piece the knife back together. He's in the second year of his physics and philosophy course at Oxford (where else would he go) because they let him in early once they read his desperate application letter. It wasn't routine or regulation but not much about Will's life has ever followed either of those two words.
He's twenty when he feels the tug in his lower stomach that he remembers from when he was twelve. The knife is in his hand and if he presses carefully he can feel the resistance of a door. He doesn't make the cut, though. He still has something to figure out before he can make his way back to his heart.
He's twenty-one when he finally manages to pull his research together for his final year. His professor had raised her eyebrows at his chosen topic because he forgot the right word for it in the world and said he was going to write his paper on Dust, but the work has paid off because he's figured out how to stop so much of it escaping.
He's twenty-two when the last issue is solved, when he works out how to stop the Spectres slipping out from the seams of open worlds. He doesn't know how he gets to the solution, he just knows in his stomach, the same way he knew how to use the knife in the first place.
It's not until he's twenty-four that he dares to use it. With Kirjava at his heels, he opens an invisible door and steps through into a memory. It's not quite the same anymore, however. The city is Cittágazze, the city of magpies, although when Will had learned enough Italian, he began to think if it as Cittáraggazze: the City of Children. Now it is no longer just the city of children and is populated with more than the few urchins that were here last time. Laughter floats out of family homes and he allows himself a small smile. The Spectres won't be an issue anymore.
He's twenty-five by the time he goes any further than the old city between worlds.
It's June 23rd when he steps into an Oxford only fractionally different from his own. It's not hard to find the hotel halfway between the Botanical Gardens and Jordan College because it's halfway between the Botanical Gardens and his own College, Exeter College, back in the Oxford that he came from. (He doesn't know if she's still there now, of course, but he knows where she'll be tomorrow.) He stays in his rooms for as long as he can, but Kirjava can only calm him so much, and at one o'clock in the morning, they both slip out of their window and in through the locked gates of the Botanical Gardens. He worked out how to do it years ago at home, and the security here is not so different as to require a new tactic. He waits in silence, with the two fingers of his left hand buried in Kirjava's fur.
It's June 24th when he hears quite footsteps behind him and a strangled gasp. He's on his feet immediately, staring at the tall young woman in front of him. Her frizzy hair is tied back with a ribbon and there's a lithe pine marten wrapped over her shoulders. The blue of her light coat complements her dark skin and her cheeks are flushed slightly. She takes a shaky step towards him, half gasps his name and then falls into his arms.
It's been thirteen years since they saw each other—far too long for both of them—and there is so much to catch up on. They have time, however, so for now they return to the same bench they had almost met at every year. Their daemons are entwined on their laps and the midsummer sky stretches above them like the years that stretch in their future. One day soon, they will have to leave each other again, but now they know that it won't be the last time and their souls don't hurt as much.
They're both ninety-seven when they slip through their last doorway with enough stories to last until the end of time.