Another shifter colony.
H intersects with dark Fae trapped here and trying to get home via a spell requiring the blood of a shifter. The fae is targeting the h. Much confusion about what's going on, coupled with H/h's blossoming relationship, interspersed with mayhem over the border. With a side order of the h's brother stalking a half shifter currently living under the radar (didn't care for that.)
Changed my mind about waiting 'til last book for series opinions. Will add as I go along.
Collars work off adrenaline. There are far more sources of adrenaline than fighting. In fact, as was demonstrated in BodyGuard, one can keep emotion out of it and still fight. One can also get so angry that the shock doesn't register.