When Layton receives the first letter from Lady Dahlia, he ignores it. Rushing around solving puzzles was something that the old Hershel Layton did. Rushing around solving puzzles is something to be done with an assistant, and Layton has no plans to replace Luke.
The second request is likewise ignored, but when the third comes, more forceful than the last two, he resigns himself. Perhaps, at least, if he gains some sort of treasure he can donate it to the fund Luke's parents set up, in the hope that, though it can never bring Luke back, other parents can be saved from watching their own child fade away in the same way that Luke did.
He travels to St Mystere alone, solves the puzzles given to him properly, but half-heartedly. The mysteries hardly interest him, though he finds himself wondering what Luke might have made of them. He slogs through it all because he feels he has to, not because he wants to, and the closest he comes to wanting something the entire time is, though he hates to think about it, a vague wish that he could have let that ferris wheel hit him so that he might have ended up with Luke.
When he finds the girl at the top of the tower, realises what the Baron's intent was with the whole mystery, Layton wishes he'd ignored all the damn letters.
He takes Flora down from the tower before Don Paulo can destroy it, passes her to one of the villagers and leaves before anyone can notice he's gone. He decided when Luke died that he'd never put himself at risk of that again, he'd never replace Luke. Besides, robots or no, Flora has an entire village to look after her.
After St Mystere, Layton stops answering letters, and stops even reading most of them. Unless he knows it's something necessary, such as bills or letters from the university, it's simpler to just sweep them away and pretend they never arrived. It's easier to ensure he'll never again be put in a situation like the one with Flora.
He's curious when he recognises the handwriting on one of the letters as belonging to Schrader, but he knows that if he gives in, reads one, the dam will burst and he'll read them all, end up dragged into isomething/i that he's not prepared to deal with. So he ignores that one too, sweeps it aside and puts on a record to let the music put it out of his mind.
He hears a few things on the radio about the great-niece of some wealthy businessman going missing from a village named Dropstone, but he pays it no mind.
Hand-delivered letters start arriving, no stamp and only 'Professor' written upon the envelopes. He ignores them pointedly, knowing full well that if he does he'll be dragged into something, until the morning that he wakes up to a weight on his bed, to a young man sitting there and watching him sleep.
He looks so much like Luke.
"I've been trying to contact you for so long, professor," the man murmurs, leaning in towards Layton now that he's obviously awake. "You ignored all my letters."
There's a hint of an accent there, a ghost of something that Layton can't even be sure is really there, that he knows he wants because this man looks so much like Luke, so much like what could have been, and sick as it may be he wants to pretend for a while that maybe this could be Luke, that perhaps he can spend a short time not worrying about replacing Luke because this could be Luke.
Layton says nothing.
"If you had bothered to read them, though," the man continues, "You might have been more prepared for this. Now, of course, I'm forced to explain this entire situation from the start in a manner that I had never intended to have to."
"I'll ask you to remain quiet for my explanation, though, professor; I'm well aware that you'll have a great many questions, but if I allow you to actually voice them at the current time I rather suspect I'll never actually finish."
Without waiting for Layton to agree or disagree, he goes on.
"You may or may not be familiar with the concept of alternate universes, professor, but regardless of whether you know that they exist, they do. To pre-empt a future question, the reason that I know that for a fact is that this isn't quite the place I come from, if you understand my meaning.
"They're not quite as you'd possibly expect them, though. They're rather close to identical, from my experience, besides a few... choice differences, but - whether because they actually are, or simply because our calculations were off, they seem a little... out of sync with each other. The year here is ten years behind what I'm used to, give or take a little. Though honestly I can't tell for certain if some of the differences are a time thing or a world thing, there are differences, and changing some of those is the reason I've come to you, professor.
"You see... as odd as it feels to say this - no matter that it's been true for rather a long time and is utterly undeniable for me - where I'm from, you are, for lack of a better word, evil. I don 't know if I can truly change it, but... well. If anyone can stop it, another version of you can, Professor."
He watches Layton, gives him an odd little look and when Layton says that name he just nods, leans in and lets the professor embrace him. Knots his hand in Layton's hair, pulls him closer, and though Layton can't tell who makes the first movement to touch lips it hardly matters because they're certainly both continuing it, this Luke so forceful and clever and so Luke, all vibrant and boyish and alive. The way his Luke could have been. Should have been.
He can't not agree to help, when they pull apart and Luke asks again, because the thought of another him who still has Luke and is so absorbed in his own ideals to even realise how damn lucky he is makes Layton feel sick to his stomach.
No matter how sick he'd felt at the thought of another him treating another Luke, a living Luke with anything less than the pure adoration Layton felt for him, nothing compares to the realisation.
It doesn't truly hit him until after Claire has gone, and he's standing alone in an alleyway and oh god, Luke is gone again, he has to tell himself that all over again. Had it been true, he'd known the parting would have been difficult, that that other Luke would have to go home and Layton would be alone again, but he would have been alone knowing that there was another Luke out there, one who had survived, one whose life had been improved even if just a little by the actions of this Layton, to stop the other Layton.
Except it's all a lie.
He turns before he's even truly comprehended the cough behind him, and there's Clive, handcuffs hanging limply because the chain's split in half (he's snapped it, Layton notes, the analytical part of his brain that can't shut off even now). Just standing there, and when he opens his mouth to say something Layton lurches forward.
Punches him.
Clive clearly wasn't expecting it, and he reels back, eyes wide, but Layton rails on him. Voice hushed despite himself, because he cannot make a scene, because he's a true gentleman, because he can't risk them carting Clive off before he's finished. Clive crossed a line, Clive made him hope, Clive was the first person he ever let himself feel with in the same way since Claire, and only because Clive was Luke and now they're both gone all over again in one night and does Clive not understand that it's too damn much after everything else?
When Clive pushes him against the wall and kisses him though, pulls back to watch Layton with a bruise already flowering impressively on his cheek, Layton finds he can't bring himself to fight any more.
He's so tired now.
And Clive is still so much like Luke.
Which is probably why the next morning finds them driving out of London in the Laytonmobile, the belongings Layton can't bear to leave shoved in the boot and on the back seat along with a few things Clive was able to grab in a brief stop at his apartment on the way out. Clive in black because Layton can't yet bear to see him in blue again, both of them breathless and giddy because good god Clive is a wanted man, and it's one thing for Clive to have wanted to speak to Layton last night, another for him to be continuing with some sort of pre-jail jailbreak, and another entirely for Layton to be helping him.
He doesn't know why he's doing it.
Perhaps because Clive still resembles Luke so much, perhaps because Layton needs to be able to see Clive as his own person before he can truly forgive him or condemn him for what he did. Perhaps simply because, bombing it out of London with Clive huddled in the passenger seat, both of them on the lookout for the police, knowing that if they're caught they'll both be (to use Clive's less-than-gentlemanly summation) well and truly fucked, Layton has never felt quite so alive.
He hasn't forgiven Clive for what he did, not even close, but Layton plans to have the opportunity to make that decision entirely for himself. Luke may be gone, but Clive is here. Not a replacement, not the same any more, not an assistant or apprentice, but certainly a potential companion.
Despite all the efforts Layton made to teach Luke to be gentlemanly, he rather suspects Luke would approve of Layton moving on even at the expense of the law, if he could.
Rather suspects Luke does approve, wherever he is.