There are 2 books in the The Sixth World series. The newest book is Storm of Locusts which came out in 2019.

1
Trail of Lightning

Book cover of Trail of Lightning
One of the Time 100 Best Fantasy Books Of All Time

2019 LOCUS AWARD WINNER, BEST FIRST NOVEL

2019 HUGO AWARD FINALIST, BEST NOVEL

Nebula Award Finalist for Best Novel

One of Bustle's Top 20 "landmark sci-fi and fantasy novels" of the decade

"Someone please cancel Supernatural already and give…
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2
Storm of Locusts

Book cover of Storm of Locusts
Kai and Caleb Goodacre have been kidnapped just as rumors of a cult sweeping across the reservation leads Maggie and Hastiin to investigate an outpost, and what they find there will challenge everything they've come to know in this "badass" (The New York Times) action-packed sequel to Trail of Lightning.…