Dear Mark,
I hope you have had a relaxing week since I headed home. I just wanted to say a massive thank you for hosting me last weekend; it was honestly the highlight of my month to catch up and explore the city together again.
However, I am writing to you with a sheepish confession. When I was packing my suitcase in such a rush on Sunday morning, I accidentally slipped your vintage leather fountain pen into my bag. I am not entirely sure how it happened, but I suspect it was lying on the bedside table next to my own notebook, and I must have swept them both up without checking.
I feel terrible about taking something so personal of yours. I have already wrapped it securely in bubble wrap and a padded envelope. I am planning to drop it off at the post office tomorrow morning via tracked delivery, so it should be back with you by Wednesday at the latest. Please let me know if it arrives safely.
Let’s make sure we plan our next get-together soon, hopefully with fewer complications next time!
Best wishes,
Sarah