Deep Sea Diver, Robot, and Monkey board a submarine, the Guppy, to delve into the darkest depths to discover what has taken the light from the sea.

"Meet The Secret Explorers! This group of brilliant kids comes together from all four corners of the globe to fix problems, solve mysteries, and gather knowledge all over the planet - and beyond. Whenever their help is needed, a special sign will appear on a door. They step through to the Exploration Station and receive their mission... In The Lost Whales, marine life expert Connor needs to use his underwater expertise to help save a pod of humpback...

In this wordless picture book, a student is accidentally left behind on a field trip to the ocean deep.