Lucy knew it, and it exasperated her to say something more, but she was prevented by St.Leon's rising to go.

As Lucy accompanied him to the door she asked how long he intended to remain in S----.
"I leave this evening, in the cars for New Haven," said he.
"This evening ?" repeated Lucy in a disappointed tone, "and will you not return ?" "Yes, if the business on which I go is successful," answered St.Leon.
"A lady in question, perchance," remarked Lucy playfully.
"You interpret the truth accurately," said St.Leon, and with a cold, polite bow he was gone.
"Why was he going to New Haven ?" This was the thought which now tortured Lucy.

He had confessed that a lady was concerned in his going, but who was she, and what was she to him?
Anyway, there was a comfort in knowing that Ada Harcourt had nothing to do with it! Mistaken Lucy! Ada Harcourt had everything to do with it!.