In Lost Secret of the Rainforest (aka EcoQuest II, though this does not appear in the game's title), the second installment in the series, Adam, now slightly older and able to speak with animals as a matter of course, explores the tropical rainforest in search of a cure of a disease afflicting the local Indigenous peoples of South America, and a way to save the rainforest from destruction. The game introduces children ages 12 and up to marine biology and marine conservation by confronting them with the consequences of various human activities including: dumping of litter, releasing of helium-filled balloons, abandonment of fishing gear, collisions between vessels and marine mammals, spilling of oil and chemicals into the sea and the fertilization of algal blooms. The Search for Cetus introduced the recycling symbol to Sierra's standard palette of command icons, giving the player bonus points for removing litter from the marine environment. The game presents the player with practical, narrative problems to solve (typical of Sierra adventure games of the period) combined with occasional puzzle elements similar to those found in the Castle of Dr. Aside from the considerable liberty of sentient talking and semi- anthropomorphic animals, the game is more realistic than cartoony.

He has assistance in the form of several creatures found in the various ecosystems of the world. In no time flat, he's trying to seek out Cetus, the sperm whale king of Eluria, an underwater kingdom populated by marine animals. Adam's attempts to help a dolphin named Delphineus that his father has rescued, takes a turn for the weirder when the dolphin starts talking. The protagonist is a 10-year-old boy named Adam Greene, the son of an ecologist and an expert scuba diver. The Search for Cetus was released first on floppy disk, then on CD-ROM with full speech in 1992. Both use a fully mouse-driven version of SCI1, in the manner of Space Quest IV and King's Quest VI. The games are considerably easier than most Sierra adventures and cannot be lost or rendered unwinnable. The last of Sierra's various Quest series, EcoQuest is designed to teach about the importance of environmental ethics. A sequel, Lost Secret of the Rainforest, was released in 1993. The game was going to be ported to Amiga and Macintosh, but those releases never came out. The game designers are Jane Jensen and Gano Haine. The original concept was developed by Sierra VP of Creative Development, Bill Davis. EcoQuest: The Search for Cetus is an educational adventure game developed by Sierra On-Line.

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