Explorer Academy. The Star Dunes

"Cruz and his fellow recruits tackle challenging missions to dispense life-saving medication to gorillas, thwart pangolin poachers, and capture images of the last known cheetahs in Namibia--all the while discovering that protecting the world's threatened species is a dangerous business. Things turn deadly for Lani, Sailor, Emmett, and Cruz as they search for the fourth piece of Cruz's mom's cipher. Cruz knows it's not going to be easy, but will an unexpected guest bring a disastrous end to the search? In this global game of cat and mouse, one mistake may cost you the ultimate price"--