When Sara and Daniel's teacher implements electronic Bin Coin rewards for collecting trash and recycling, the kids start using this digital currency to buy and sell. Their developing system for keeping track of accounts brings in concepts from the world of cryptocurrency such as mining a block (recording trades that have been validated), a cryptographic nonce (a number used only once), a mempool (the memory pool for storing trades not yet validated) and a double spend attack . But then Sara and Daniel face a series of mysteries and crises: Why is this small kid paying BinCoin to the class bully in such oddly specific amounts? Can knowledge of the school's digital currency help restore a man's life savings using a real cryptocurrency? And during a visit from the State Board of Education, who pulled the fire alarm before the block could be mined?.