While staying with relatives in Rajasthan, India, Reeya Rai and her friends are playing a game of cricket when they stumble upon an ancient, water-filled stepwell. Reeya and her friends decide to create a submersible with a camera to explore the stepwell and uncover its secrets. In the watery depths, they discover an ancient door with a mysterious symbol on it. Could this be the key to discovering one of India’s ancient lost treasures? And will they uncover the truth before Dr Acker and his daughter, Elsie, learn about what they’ve found? Part of the Reeya Rai: Adventurous Inventor series.