When I first heard of Capri's Reacher books, I wasn't interested at all. I rarely read books featuring a character created by another author. But then I bought a compilation of books that included one from this series and I was hooked. When I discovered that the book I'd read was not listed as the first in the series, I went back to Amazon and found this book was labeled as #1.
The premise here is that two FBI agents are sent to the small town in Georgia that was featured in the Killing Floor, the first of the original Reacher series, some 15 years later. I think it is best to read Lee Child's book first as I think it is Capri's assumption that you have. If you do, you'll know a lot about Jack Reacher that the FBI agents are clueless about. If you want though, you can start this series here and guess along with the FBI.