The Mystery of the Lost Key

On thursday, my dad transported one of his/mine mountain bikes to my residence, the beautiful city of Leiden. It had been a year or so since I had an operational bike. Finally, I could go places without having the tedious job of walking there. I went to the ‘Albert Heijn XL’ (some oversized supermarket about 1 km from home). I went to work on it. Now, my dad has asked...