More Than You Know (The Solars Duology, Book 1). The Solars Duology, #1

Avery Kale is a paranormal law enforcement agent in charge of rogue solars-people who use their ability to harness the sun to commit crimes. Her husband Reed is a teacher, helping young solars adapt to becoming part of the solar community. Their marriage has been a delicate equilibrium ever since their deadly allergy to each other nearly killed Reed, a balancing act neither is able to endure much longer.
But Reed's insistence on finding a better solution wars with Avery's fear that trying could be fatal. Then Avery and Reed are enlisted for a multi-jurisdictional homicide case. Someone has been using heretofore unknown powers to kill using the sun. They need Avery's unique ability to determine if their main suspect is a solar. Paul Adranian, a DC billionaire, is hiring a husband-wife bodyguard team for his kids, and Avery and Reed are the task force's best option.
The risk seems low: Get hired, get in, identify him, and get out. But the not-so-quick job drags on and gets complicated when Paul enlists them to clear his name, using an enticement they can't turn down. Now not only are Avery and Reed targets of the most dangerous solar ever known and a danger to each other, being together every day has put a spotlight on problems they didn't know they had. If they survive the killer and the allergy.is their marriage doomed anyway?