The old green door to the masjid library is locked, and the key has vanished. Weekend school is about to begin, the younger class is waiting for story circle, and the children must solve the mystery before the library can open. But this is not an ordinary treasure hunt. Each clue teaches an Islamic value: patience, trust, honesty, service, sadaqah, teamwork, and good adab. In this choose-your-path adventure, young readers decide where to search, who to trust, and how to act when the answer is not obvious. Some choices lead to the best ending. Others teach a lesson and let the reader try again. The Lost Masjid Key is a gentle Islamic mystery adventure for children aged 6–8, ideal for family reading, Islamic weekend school, homeschool, classroom use, and early independent readers. A warm, faith-friendly story about solving problems with kindness, asking before touching, telling the truth, avoiding blame, and leaving places better than you found them.