Fatal Dose, the second Cliff Knowles Mystery in the geocaching trilogy, is free today in Kindle form. If you don't have a Kindle, there are free Kindle apps for Android, Apple and Microsoft phones, tablets etc. Geocaching is not as heavily integrated in the plot as it is in Cached Out and Death Row, but the geocaching scenes in Fatal Dose are important in the character development and relationships. The free day is California time, so it will end soon in the UK.
http://www.amazon.co.uk/Fatal-Dose-Cliff-Knowles-Mystery-ebook/dp/B00F70SZXW/