Promise of Danger by Meg Anne

Her promise just might be his undoing. To save Nord, Lina would do anything. Even bloodswear a vow to the infamous King of the Underground. But when Crombie comes to collect, no one is prepared for the chain of events he sets off. Now she’s missing, and Quinn and Finley must help Nord before he tears the world apart in his search for her. Because when a berserker’s mate is in jeopardy, there’s no line he won’t cross, no sin he won’t commit, to rescue her. Only a fool—or a fae prince—would be stupid enough to invoke a berserker’s wrath. And now, everyone must answer to the monster he unleashed.