The Elly Griffiths books are 9.99-14.85 at Amazon, but they are couponable at Kobo.
Here's a free Griffiths short story from Houghton Mifflin Harcourt:
Ruth's First Christmas (Ruth Galloway Mysteries) by Elly Griffiths
Kobo US:
http://store.kobobooks.com/en-US/ebo...irst-christmas
Amazon US:
http://www.amazon.com/dp/B00AFDUN72
Edit: it is a kepub at Kobo with no download button.