The adventure intensifies at a breakneck pace to the shocking conclusion of the Rio Grande Parallax series. Impossible odds face two groups of comrades who have traveled far seeking answers to mysteries. The first company heads for the Saddle of the Mountains of the Sky while the second, a hundred miles to the west on the barren Malpais, is led by Esther. Both groups face deadly enemies and startling enigmas. Back in Rio Luna, Esther's mysterious disappearance confounds her parents and her friend, Markey. In the Valle, though, questions surrounding Don are resolved. Meanwhile, the Soreyes heap new terrors on the clanspeople. Will the travelers return in time? Facing challenges far more insurmountable than bringing down the Tower of Il Serrohe, can the hapless clanspeople dare hope for freedom?