Heroine (not named yet) is part of a search-and-rescue team run by her adopted family. When a plane carrying a child in need of a transplant crash-lands on their mountain in a storm, an outside team of rescuers joins the effort. The hero (unnamed so far) is another member of the Hunt. Heroine isn't happy to be reminded of the duty imposed on all the members of the Hunt when they were sent to Earth for safekeeping. The hero is persistent. When the Hounds appear, sparks start to fly and causes disruptions in her ordinary, settled life, including straining her relationship with her new boyfriend. In the end, she has to make a choice, and just barely chooses duty before they are contacted by other members of the Hunt -- main characters in the previous 3 stories -- and learn that time is running out for them. Earth isn't entirely friendly to the visitors from another dimension/parallel universe, and as they get older they will grow ill. They can't stay on Earth.
Not happy news, but it makes her hard decision a little easier. Especially as Gahlmorag, the enemy of their homeworld, is on the verge of breaking the dimensional barrier and finding them on Earth.