Illusion of a Boar. Land Mysteries, #5

In March of 1944, four magical specialists are brought together at a secret camp for an even more mysterious mission.  Hypatia and Cammie adopted each other as sisters twenty years ago, during their school years, after Cammie's mother married Hypatia's older brother. Cammie has been neck deep in signals work since the start of the Second World War, while Hypatia has used her gift for sympathetic magic and materia to support the war effort.
All while keeping up the proper standards for ATS girls, of course.  Pulled from similar work in Scotland, Claudio knows the most about what's needed and about what resources might actually be available. That's a big problem, but he's far more worried about his chosen brother, Orion. Orion's war had been comparatively simple until six months ago. After an injury invalided him out of active service using his magic to support the front lines in the Mediterranean, he came home to find betrayal.
Now he's figuring out where to begin rebuilding any sense of himself and his place in the world. None of them have enough information or access to resources for what they're being asked to do. And they're doing it in a camp that has no idea what to make of them and that has its own deep secrets. When the challenges keep coming, they have to figure out whether and how they can trust each other and whether their objective is even possible.  Illusion of a Boar takes on the run-up to D-Day inside the magical community of Albion, figuring out what magic could help turn the tides in their favour.
It's about trust, choosing new paths, and just maybe taking a chance on love and romance. The fifth book in the Land Mysteries series, it can be read in any order.