Around Curiosity’s Edge (Raging Waters #2)

A DARK ARMY RISES,
A NEW SHIP SAILS THE SEAS,
AND OLD ONES, LONG SILENT,
ARE SUMMONED FORTH TO LEAD.
Whereas only a few months earlier he would not have believed any of it, Salem Swan now finds himself faced with sinister enemies and, equally surreal, surrounded by close friends. He has gained powers as a mythlinguist, and with it a responsibility to reunite the world of humans with the world of myth, known as the Fringe.
With his uncle Ulysses and Captain Fern taken prisoner by a growing Regulat force, it's up to Salem and the crew to seek help in old allies. This takes them to the heart of the Amazonian rainforest, where a city concealed in waterfalls tests the measure of their resolve.
Meanwhile Regulat forces conspire to eliminate fringers of the World Beneath and bear down on a sacred space with a terrible force that knows no mercy.
The world is changing faster than anyone realizes, and salvaging its best parts now rests in the hands of three teenagers and a mythical crew who cannot stand to see it lost.