Arnold, delayed in getting away at his own time, from his own property, by ceremonies incidental to his position which were not to be abridged without giving offense to many worthy people--had caught the passing train early that morning at the station nearest to him, and had returned to Lady Lundie's, as he had left Lady Lundie's, in company with his friend.
After a short preliminary interview with Blanche, Arnold had rejoined Geoffrey in the safe retirement of the library, to say what was still left to be said between them on the subject of Anne.

Having completed his report of events at Craig Fernie, he was now naturally waiting to hear what Geoffrey had to say on his side.

To Arnold's astonishment, Geoffrey coolly turned away to leave the library without uttering a word.
Arnold stopped him without ceremony.
"Not quite so fast, Geoffrey," he said.

"I have an interest in Miss Silvester's welfare as well as in yours.

Now you are back again in Scotland, what are you going to do ?" If Geoffrey had told the truth, he must have stated his position much as follows: He had necessarily decided on deserting Anne when he had decided on joining his brother on the journey back.