The Tempting of Tavernake by E. Phillips Oppenheim

Tavernake awoke some hours later with a puzzled sense of having lost his own identity, of having taken up another man's life, stepped into another man's shoes. From the day of his first arrival in London, a raw country youth, till the night when he had spoken to Beatrice on the roof of Blenheim House, nothing that could properly be called an adventure had ever happened to him. He had never for a moment felt the want of it; he had not even indulged in the reading of books of romance. The thing which had happened last night, as in the cold morning sunlight he sat up in his bed, seemed to him a thing grotesque, inconceivable. It was not really possible that those people -- those well-bred, well-looking people -- had seriously contemplated an enormity which seemed to belong to the back pages of history, or that he, Tavernake, had burst through a wall with no weapons in his hand, and had dominated the situation! He sat there steadily thinking. It was incredible, but it was true!

There existed still in his mind some faint doubt as to whether they would really have proceeded to extremities. Pritchard himself had made light of the whole affair, afterwards had treated it, indeed, as a huge practical joke. Tavernake, remembering that little group as he had first seen it, remained doubtful.