因未能及时还书致歉Unable to return borrowed book on time 

Dear Kate: 

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. 

Sincerely yours, 

Tom