Fearless by Kelly Goode

The aliens didn’t invade Earth as depicted in the movies – they were smarter than that.
Doctor Helen Peters is a woman of science and medicine, and it’s not until she’s kidnapped by an alien that she discovers the truth about the creatures that have been living undetected on Earth for centuries.

Viktor was a prince on his home planet, and since crash-landing on Earth, has dedicated his life to protecting his colony’s secrets. He hates humans. Except a certain red-headed doctor has caused him to question everything he knew about inter-species relationships. He stole her away from her people, but she may steal something of her own in return – his heart. Return to the Invasive Species Control Unit, where defeating the aliens should be their hardest mission, but trying not to fall in love with them is proving trickier.