Pirate adjacent coming of age book
I read this book in middle school and remember really liking it, the main character was a young boy who lived with his dad and If I remember correctly his mother had passed. His best friend had a photographic memory and they discovered a kind of treasure map. They used a hidden passageway in the house to explore what I think was the sewer system and on the way to find the treasure they found a boy who was living underground. I believe there was a group of cia agents or mercenaries underground with them competing to find the treasure.
There was also a bit of dialogue in the book I remember where the main character explained that 20 minutes is about how long it takes for your eyes to adjust to the darkness.
I’ve been searching for this book forever and I’ve built up how good it was in my head so I gotta read it again, I really appreciate any help!