How instantly would a knowledge of its contents have affected all the purposes that were now leading him on with almost the blindness of infatuation.

The man he was trusting so implicitly would have instantly stood revealed as a scheming, unprincipled adventurer.

In such estimation, at least, he must have been held by Mr.Markland, and his future actions would have been governed by that estimate.
The answer to Fanny's earnest, almost peremptory demand, to be released from the injunction not to tell her parents of Mr.Lyon's return, was in her possession, and the instant she could get away to her own room, she tore the letter open.

The reader already knows its contents.

The effect upon her was paralyzing.