Immortal by VE Duncan

Kait Peters is a normal Mortal living a normal life until an accident on a rain-slicked road exposes her to a deadly parasite—and a secret world. Kait soon suspects the questions haunting her since that night could reveal secrets more dangerous than anything she could have imagined. Jackson Cunningham is the enigmatic stranger who helps Kait on that fateful night. But he's also an Immortal, infected with a parasite bestowing superhuman abilities at a terrible price. It’s his fault Kait was exposed. Duty-bound to observe her for signs of infection, he must also conceal from her the existence of the underground world of Immortals. But how can he do that when Kait sees through his carefully constructed lies? Meanwhile, a rogue Immortal is hunting Mortals and committing the unspeakable act of infecting them with the immortality parasite. Could Jackson’s pursuit of the rogue put Kait in the madman’s crosshairs? Jackson and Kait must fight to protect each other and those they care about. As they grow closer, they must also navigate the web of lies and half-truths keeping them apart. Can their love survive the collision of two worlds?