STINGRAY CITY

When the stingray population at a famed Grand Cayman attraction plummets mysteriously, it’s time to call in the Sea Guardians.

Once again, 13-year-old Tristan and his fellow campers do a terrible job of keeping their drug-enhanced abilities to talk to sea life and other watery feats secret (The Shark Rider, 2015, etc.). This time it works out, as the diver they rescue in Monterey Bay turns out to be Leo Ozdale, a wealthy conservationist and inventor who later summons them to the Caribbean to track down the missing rays. Following clues gathered from the remaining rays (in dialect, continuing the series’ questionable use thereof: “Ya, mon”; “Whoa, bobo!”), the Guardians ultimately zero in on illegal collectors aboard a secretly modified cargo ship crewed (why be subtle?) by smelly toughs with bad teeth led by a bullwhip-cracking “queen of mean.” Captures, escapes, and undersea heroics ensue. The caper is a slapped-together affair made up of set pieces with sudden transitions (sometimes monthslong), a mostly white cast of teens (there is one Latina), and an anticlimactic nab that takes place offstage. It does provide bits of comedy, drama, and budding romance, though, amid the discussions of issues related to keeping captive animals, as well as a series of vividly described encounters with marine wonders. Illustrations not seen.

Eco-sleuths triumph again, but it might be just as well to send them to retirement now.