OSS Wilderness is the fourth book in the Spy Kids Adventures series.
Carmen and Juni are spending the summer at an OSS sleep-away camp. The camp director is a retired spy-turned-environmentalist named Oscar Zohn. But it turns out that O. Zohn thinks environmentalism means using nature for his own devices. He plans on using the unknowing help of the Spy Kid campers. Only Carmen and Juni are in the know…which means only they can help!