Annihilation by Jeff Vandermeer is only $2.99 this week
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Book one of the Southern Reach Trilogy. I've read this and the second book (Authority) and really enjoyed them both. It's like literary SF horror (think of something like Lovecraft meets Kafka meets naturalist Edward O. Wilson).
Area X has been cut off from the rest of the continent for decades. Nature has reclaimed the last vestiges of human civilization. The first expedition returned with reports of a pristine, Edenic landscape; the second expedition ended in mass suicide, the third expedition in a hail of gunfire as its members turned on one another. The members of the eleventh expedition returned as shadows of their former selves, and within weeks, all had died of cancer. In Annihilation, the first volume of Jeff VanderMeer's Southern Reach trilogy, we join the twelfth expedition.