The Higher Elevation Box Set includes books one through three of this series.
I will be honest; I had a difficult time with the first part of book one. It felt like it moved slowly and I had a challenge getting into the story. I stuck it out though, and it turned out to be a great read. I loved the period references of the VW and the eight track tapes, lol.
A plus for getting this box set is that you get to binge read it! This series contains all of the things that make a story great-mystery, suspense, danger, romance, and a little sci-fi. It is a great escape for a few hours.