This Volume begins with a previous expedition across North America, where they explorers have a lot of bad luck, from being attacked by man-eating insects, killer grass and river creatures. One of the survivors encounters the ghost of a Spanish explorer, who has a weird effect on him. Then, in 1804, the Lewis and Clark expedition encounters those same travails, with much better luck at defending themselves. The primary creature introduced is a race of cyclops, which the writer crosses with the legend of Sasquatch. The survivor from 1801, via the direction of the ghost, kills one of the creatures and is encouraged to eat it. He finds it delicious. He wants the others in his group to eat it as well, though it has an unforseen consequence. It turns out that these creatures are mostly peaceful and it's the humans who are monsters.
Another creature is also introduced, a scaled, dragon-like entity called Navath.
This volume is as entertaining as the previous three, though I felt it's getting a bit repetitive and a little bit more fantastical.