Gathering Storm is one of Richard Castle's very successful Derrick Storm novels, written by Castle in the years before he met Beckett. Although referenced in the show, unlike some other Storm books, it has never been made available in the real world.
(from richardcastle.net) While packing his bags for a much-needed vacation, Storm gets a call from CIA Agent Clara Strike with an urgent mission. Storm must help protect the Swiss ambassador’s daughter against a formidable foe: a former KGB officer who is known for killing his victims with undetectable poison. When the mission is compromised, Clara fears that there is a mole in the CIA. In a bold move, Clara decides to put Storm undercover at Langley in order to smoke out the guilty party. Unexpectedly, Storm does more than just that; he uncovers a conspiracy that goes to the top levels of the agency and threatens Clara’s livelihood.
References in Episodes
Flowers For Your Grave (episode 1.1): seen in Kyle's apartment – there are two different spines shown with this title