Below Zero is a sequel to Box's third Joe Pickett novel Winterkill. Well it's a sequel to 7 others as well, but the ending of those ones isn't given away as Winterkill's plot is in Below Zero. So I'd highly recommend reading that one first, in fact, I'd suggest reading the whole series in order which starts with Open Season. Their order is at the bottom of this review. All can be read as standalone reads, but once you've read one, you'll want to read them all so you might as well read them in order and experience Pickett's family grow and his career, well not really grow but you'll experience it's ups and downs.
In Below Zero, a school boy now living in the Pickett family's old home, trying to impress Joe's daughter, passes her mobile number onto a mysterious caller. That caller will shortly after text Sheridan claiming she is April, a foster sister who the family thought was dead. Meanwhile Joe posted to the outskirts of the state for his past actions (read the former novels) is out to apprehend after rescuing a victim, the Mad Archer, a particularly grade A environmental lowlife, who seems to enjoy shooting arrows into wildlife and leaving them to die. When Joe learns of the texts to his daughter, he immediately takes personal leave and rushes back, set to do whatever he can to find out if April is April, which doesn't seem likely. When he learns the girl claims she is travelling with two men who are doing bad things such as killing people (unbeknownst to Pickett killing in the name of reducing carbon footprints of those who substantially pollute with no regard for the planet), he is determined to rescue her this time round.
1. Open Season (2001)
2. Savage Run (2002)
3. Winterkill (2003)
4. Trophy Hunt (2004)
5. Out of Range (2005)
6. In Plain Sight (2006)
7. Free Fire (2007)
8. Blood Trail (2008)
9. Below Zero (2009)
10. Nowhere to Run (2010)
If you've read all the Joe Pickett novels, I'd also suggest the author Ben Rehder. Buck Fever is book one in a series of adventures set in Blanco County Texas with a very similar character to Joe Pickett in game warden John Marlin who could practically be his twin separated at birth and sent to Texas.