Leslie's grandfather, Captain Clark, has taken the ClueFinders to the South Pacific, where they are investigating a Brand X version of The Bermuda Triangle. After their ship is hit by a tsunami, Joni, Santiago, and LapTrap wake up on the beach of a tiny volcanic island. However, everyone else from the ship has mysteriously disappeared. It therefore falls to Joni, Santiago, and LapTrap to find and rescue the others.
The game begins with you being able to explore two areas, the surface of the island and underwater. The island is inhabited by centuries of trapped castaways while the underwater area is inhabited by talking tubeworms. Both claim that the island itself is somehow alive and has been continuously thwarting all attempts at escape. Your only hope is to collect CrypTiles, which are metal plates carved with odd symbols. You'll need them to gain access to the game's third area, the inside of the island, where you'll rescue the others and discover the truth about this strange place.
This game provides examples of:
- Adults Are Useless: Centuries of castaways were apparently unable to get past the Faces within the Face or the Fish within the Fish, but then the ClueFinders came along. You could argue that it's because the ClueFinders were the first castaways to have modern diving equipment, giving them access to both, but that still doesn't explain why no one on the surface cracked the Faces within the Face or none of the intelligent worms cracked the Fish within the Fish. And the ClueFinders apparently do it all on the first day that they arrive on the island.
- Artistic License Geography: Lines between two locations on the map in Poison Garden activity are portrayed as straight, even though the maps' distortion would make said lines curved.
- Artistic License Geology: It's obviously impossible for an island to be simultaneously floating and actively volcanic. Ultimately justified, because the island is actually a disguised spaceship.
- Ask a Stupid Question...:Great CrypTile Thief: I'm the Great CrypTile Thief! I stole everybody's CrypTiles and buried them in my patch of dangerous trees.
Santiago: Why are you locked in the pillory?
Great CrypTile Thief: [very dryly] I got caught.
- Brain Food: The aliens are trying to collect specimens from Earth that they can cultivate and harvest for their brains back on their homeworld because they're apparently an alien delicacy.
- Closed Circle: The island has been thwarting all escape attempts for centuries. The CrypTile stories often mention people trying to leave only for the waves to form giant hands that throw them back to the shore. LapTrap's attempt to flee at the beginning of the game was thwarted by an ordinary wave.
- Creator Provincialism: Despite the CrypTile stories informing us that people from all over the world have been getting shipwrecked on this island, the two castaways who preside over a Mini-Game are both from periods of U.S. history, specifically The American Revolution and The American Civil War. Notably, most foreign localizations change them to being from the equivalent periods in that country's history.
- Developers' Foresight: Check the map at the end of the game. "Sorry! But we are now, trapped, inside!"
- Doomed by Canon: The CrypTile stories sometimes describe past escape attempts. Since no one has ever managed to escape from the island, you know right from the start that these attempts are doomed to fail.
- Enemy Mine: The CrypTile stories often have this theme, describing how the castaways have come from all over the world and how they must overcome their difference and work together.
- Face Palm: Santiago gets one at the end.
- Generation Xerox: The apparent reason why the human residents of the island still act and dress like they're from the time periods when their ancestors wound up there.
- Genius Loci: The castaways claim that the island itself is a living malevolent entity. It's actually an alien spaceship.
- Gentleman Thief: Crime has caught up with the one in the game; he's in a stockade. He buried a lot of cryptiles in a patch of Man Eating Plants, and given your need is willing to loan you the maps.
- Island of Mystery: The game's setting. The island is uncharted and full of castaways and strange phenomena.
- Lampshade Hanging: During the spelling catwalks challenge:Owen: Why is it that wherever we go, we always find large pits to cross?
- The Last of These Is Not Like the Others:Joni: LapTrap, scoop up the artifact and head on back.
LapTrap: [grumbling to himself] "Scoop up the artifact, LapTrap." "Fix the minisub, LapTrap." "Blow-dry my hair, LapTrap."
- Microts: The aliens use a time unit called a "sorlax," which is equivalent to about fifty Earth years.
- Nothing Is Scarier: Open the map during the third act. It becomes much much scarier as you see nothing, and all you get is Laptrap panicking that they are trapped inside.
- Parody Names: According to the game credits, the Civil War lady is named Charlotte No-Haira, parodying the name of Scarlett O'Hara.
- People Jars: The aliens keep humans and animals in a type of these before they eat their brains.
- Recycled Animation: Many of Joni and Santiago's animations are recycled from 3rd Grade Adventures. It's especially noticeable because Joni went through a subtle redesign, making her appear slightly older and more feminine, but she reverts to her older look when she's in a recycled animation.
- Screen Shake: At random points in the game, the screen will shake to indicate an earthquake, so that you don't forget that you're on an active volcano.Santiago: Whoa, volcano's gonna blow!
Joni: Where's the Coast Guard when you need 'em?
LapTrap: I don't like volcanoes.
- Shout-Out: If her name wasn't enough of a reference, Charlotte No-Haira also mentions that "tomorrow is another day" and how she adores "the kindness of strangers." Incidentally, the game's U.K. edition keeps these lines, despite redubbing her with a British voice and thus losing the Southern Belle accent. Ironic that Vivien Leigh, who originated both lines, was British in real life.
- Standard Snippet: "Aloha 'Oe" is briefly sung by LapTrap of all characters when he thinks they'll be able to take the minisub back to Honolulu.
- Stock Punishment: The Great CrypTile Thief is receiving this punishment, as Santiago so helpfully observes.
- Take Your Time: The game constantly teases the threat of the volcano erupting if you don't get off the island in time. Regardless, the eruption won't actually occur until the concluding cutscene.
- That's No Moon!: This island is a bit unusual, to say the least. It's a spaceship, and the aliens have been harvesting human brains.
- Tropical Island Adventure: The entire game is about the ClueFinders getting shipwrecked on a tropical island.
- Under the Sea: One of the game's main areas is underwater, which you're able to access after Joni and Santiago find their scuba gear on Captain Clark's wrecked ship.
- Unobtainium: The Cryptiles are made of an unknown substance with bizarre properties.
- What Happened to the Mouse?: The ClueFinders games frequently end abruptly, but 5th Grade in particular leaves the most loose ends.
- Was Lab-5 ever recovered from the seafloor?
- Did the tubeworms end up "inside" when Leslie hit the tsunami button, or did they simply fall off when the spaceship shed its exterior?
- How will all the castaways, who still live like their shipwrecked ancestors, adapt to modern civilization?
- None of the cast seems to care that the brain-eating aliens are still at large.
- Wingdinglish: The CrypTile language is just English with weird letters.