Shadows and Saviors by Lexi Ostrow

A deadly bioweapon has ravaged the world, leaving behind a trail of destruction and infertility. A devastated human race is all but on the verge of extinction, with a safe haven waiting for those who can bear children.

Emma is alone. After the death of her father, she remained in the basement of her family home, unable to trust others would not harm her because she was rare. A fertile female. Survival was not always black and white. It was adapt or die. With limited options, she reaches out for help through an old radio in her basement, and when a response comes, she takes a leap of faith.
When not one, but five men show up to take her to safety, Emma is both relieved and apprehensive. Chris, Bash, Liam, Alex, and William are not just handsome, but they also seem to possess a chivalrous charm. A military unit whose sole mission was to help women get to the government safe haven.
As they set out on a treacherous journey through a broken and dead country, Emma finds herself drawn to these men in ways she never thought possible. Ways that made her question if she even understood what it was she wanted once she was safe.