The Big Finish by James W. Hall
Thorn hasn’t seen his son, Flynn, in over a year, since he disappeared into the underground with the group ELF. Flynn is determined to make an environmental difference and while staking out a hog farm looking for evidence of animal cruelty to get the farm shut down, he and the rest of the ELF group find more than they bargained for. Flynn and his group are attacked and on the run.
In the meantime, Thorn had been receiving postcards from his son, but then receives one that is different than all the rest. He and Sugarman decide that it’s time to look for Flynn and make sure he’s ok.
When they are approached by a female FBI agent, who seems to have a lot of information about ELF, Thorn decides to go with her and sends Sugarman home. Along the way, Thorn discovers that he is being lied to and is being led into a trap to capture his son.
I have enjoyed all the books in the Thorn series and look forward to the next one.
Order in Bibz.