Mode

kid

parent

Monster Down Deep

Ages

9+
Cassie is an expert beachcomber. When a royal diamond necklace is lost at sea, the whole town starts searching the sand, hoping to get lucky. But Cassie’s quest turns up something she never could have imagined, and it might just be worth more than a priceless diamond...
Ages 9+
Pages 304
Publisher Penguin Random House
Last Offered Nov 2026

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What the Book is About

Eleven-year-old Cassie Stein is spending the summer before middle school searching a San Diego beach for a missing 74-carat diamond necklace. There’s a million-dollar reward, and Cassie hopes the money could save her dad’s struggling aquarium. She also wants a fresh start after a frightening experience in the ocean left her terrified of the water.

Instead of the necklace, Cassie and her new friend TJ discover Blue, a strange fish unlike anything scientists have seen before. Even more amazing, Blue seems to understand Cassie. When he is brought to Mayim Aquarium, the discovery attracts attention, fame, and the promise of badly-needed money.

But Blue is frightened, and the people interested in buying him may not care whether he survives. Cassie must decide what matters more: the fame and money that could change her life, or protecting Blue and returning him to the ocean.

Jewish Content and Values

  • Cassie and her father are Jewish, as are Zeke and Rosie, who run Mayim Aquarium. Mayim means “water” in Hebrew.
  • The aquarium’s mission is tikkun olam (repairing the world).
  • On the anniversary of her mother’s death, Cassie and her father light a yahrzeit candle, say her name, and recite Kaddish in her memory.
  • The biblical story of Nachshon plunging courageously into the Red Sea is source of inspiration for Cassie as she faces her own fears.

Content Advisory

Cassie’s mother died in a car accident years before the story begins. Cassie has panic attacks connected to her fear of the water and lies about having a medical condition to hide them. Some characters plan to sell Blue to a laboratory where he may be killed for research. These plot points are not graphic and are age appropriate.
What the Book is About

What the Book is About

Eleven-year-old Cassie Stein is spending the summer before middle school searching a San Diego beach for a missing 74-carat diamond necklace. There’s a million-dollar reward, and Cassie hopes the money could save her dad’s struggling aquarium. She also wants a fresh start after a frightening experience in the ocean left her terrified of the water.

Instead of the necklace, Cassie and her new friend TJ discover Blue, a strange fish unlike anything scientists have seen before. Even more amazing, Blue seems to understand Cassie. When he is brought to Mayim Aquarium, the discovery attracts attention, fame, and the promise of badly-needed money.

But Blue is frightened, and the people interested in buying him may not care whether he survives. Cassie must decide what matters more: the fame and money that could change her life, or protecting Blue and returning him to the ocean.

Jewish Content and Values

  • Cassie and her father are Jewish, as are Zeke and Rosie, who run Mayim Aquarium. Mayim means “water” in Hebrew.
  • The aquarium’s mission is tikkun olam (repairing the world).
  • On the anniversary of her mother’s death, Cassie and her father light a yahrzeit candle, say her name, and recite Kaddish in her memory.
  • The biblical story of Nachshon plunging courageously into the Red Sea is source of inspiration for Cassie as she faces her own fears.

Content Advisory

Cassie’s mother died in a car accident years before the story begins. Cassie has panic attacks connected to her fear of the water and lies about having a medical condition to hide them. Some characters plan to sell Blue to a laboratory where he may be killed for research. These plot points are not graphic and are age appropriate.