Sejal's puppy eats the page in her notebook with her best ideas. Her little brother throws a tantrum over string cheese. Sometimes, Sejal wishes she could escape being a big sister. After an embarrassing snot incident, her older cousin Ash is ready to leave the planet, too.

Ash has been working on a very cool science project about a theory that it rains diamonds on Neptune. Treasure hunting on another planet sounds like the perfect out-of-this world adventure to Sejal! But getting to Neptune might be harder than she and Ash think, especially when they find a couple of stowaways in their spaceship...