It's summertime in Antiquarium and everyone has flocked to the majestic lakeside Purple Pearl Hotel, including the nefarious group of evil mad scientists, the Krenetics Research Association. They haven't given up on resurrecting their fearsome leader, Talon Sharktüth, and now, they're hot on the trail of the legendary Purple Pearl, a source of power that is rumored to be lost at the bottom of Kagloopy Lake. All they need to do now is find a mysterious creature called a Shrimpmaid, boil the lake (and everything in it) away, and pluck up the pearl!

But Millicent, Gertrude, Eugenia, and Dee-Dee are onto them, and they are determined to stop the KRA, even though they are now full pariahs in Antiquarium society. While Millicent and the gang work together to prevent the second coming of Talon Sharktüth, they discover more secrets than they bargained for - including where they came from, and who they truly are...

It's a mad science summer vacation they'll never forget!