The Emperor's Gift is the fourth full book dedicated to the Grey Knights, after a not too great trilogy.
We follow through the eyes and mind of a "young" GK, Hyperion, who seems to have quite some psychic powers, above the average knights, but also seems a bit hesitant and "thinks too much" instead of just following orders from his superiors.
Some fights against chaos forces will slowly take him to great and unforseen battles with not so good... "happenings".
I quite enjoyed this book, it is well written, has plots, secrets, thought moments, nice action... Also I think here the Grey Knights are properly depicted, as being few but really powerful, and yet only superhuman, not fully invulnerable.
Recommended if you want to expand your lore about the Emperor's finest.