Paige Turner If the last sentence in this book is any indication, then no it's not the last book in the Orphan series.
Ty Gregg Hurtwitz signed a deal back in 2019 for 3 more "Orphan X" books. "Into the Fire" would be the second book from that deal. So there is at least 1 more.
Jason Monroe It was just announced this week that the next installment of the series, titled "Prodigal Son," will be released in January of 2020.