A mysterious mark, an ancient spirit, and a message from beyond the Aether...After uncovering and destroying a Necromancer plot to take over Skye Príosún, Jess and Finn are united at last and longing to move on with their life together. But the Durupinen world has other plans.An enigmatic rune keeps revealing itself to Jess-in artwork, in dreams, and even scrawled upon the ancient stones of the Geatgrima at Fairhaven. No one can identify it, but its warning is clear: something dangerous is coming, a revelation that could end the Gateway system forever.Jess must follow the clues where they lead-forming unlikely alliances along the way. When her journey takes her at last to an ancient creature deep in the heart of the príosún, the truth she learns presents her with the most troubling question of all: what if her Durupinen gift was never really a gift at all, but something altogether darker?Soul of the Sentinel is the much-anticipated sixth installment in E.E. Holmes' spine-tingling paranormal series The Gateway Trackers.