因未能及时还书致歉Unable to return borrowed book on time
Excuse me for my long delaying in returning to you your Robinson Crusoe which I read through with great interest. I had finished reading the book and was about to return it when my cousin came to see me. Never having seen the book, She was so interested in it that I had to retain it longer. However, I hope that in view of the additional delight thus afforded by your book, you will overlook my negligence in not returning it sooner.
Thanking you again for the loan.