Ok, you're right, there isn't enough information to get past the prior implausibility of the hypothesis. I think the other characters should assume he placed tracking charms on Harry. Any explanation about tracking the troll or Hermione would result in him arriving earlier, and when questioned, the divination professor can say approximately when Quirrell started to move, which cross-referenced with Harry's recollections shows that Quirrell's actions correlate with Harry being in danger, not Hermione. However, I assume that these tracking spells can be detected, in which case, if another character attempts to detect these spells and finds none on either Harry or Hermione, the Quirrell has done something seemingly impossible. Given this, Quirrell should probably cast such a spell on Harry before this occurs to anyone.
The problem is that Quirrell can't cast any spells on Harry. And, furthermore, Quirrell really doesn't want Dumbledore to find this out - Dumbledore already knows of a certain other person with an unexpected inability to cast spells on Harry Potter, and I think the hint would probably be enough for him to put the two together.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 88-89. The previous thread has passed 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: