The truth is out there...
The Dex-Files is a compilation novel that accompanies the Experiment in Terror Series and is not to be-read as a stand-alone. In the Dex-Files we find a variety of scenes and chapters from the enigmatic Dex Foray's POV from books #1-6 in the series. Some of these scenes have been previously published, albeit from Perry's POV, while other scenes are completely new.
In addition to it not being a stand-alone, the novel also contains some major spoilers and should be read only by those who have read all the published books in the series.