In Yarros’s heartbreaking The Last Letter (Entangled, Mar.), former soldier Beckett, grieving the death of his buddy Ryan, helps Ella, Ryan’s sister, through a series of tragedies.

Ella’s daughter, Maisie, is a five-year-old with advanced neuroblastoma. How did you research her cancer and treatment?

I was really, really lucky that I had some excellent resources. The entire treatment for Maisie is actually based off what a friend of ours from flight school went through with her little boy. She gave me all of his treatment records. She sat with me and went over the entire timeline, everything that she had written down as to how the diagnosis went and how the treatments went. He was one of the first kids to actually survive using the same treatment that Maisie was given. He’s four years cancer-free right now. We’re just waiting for that fifth. I’m so, so sympathetic to the moms who have gone through this. I can’t tell you how many blogs I bawled at hoping that they would have different outcomes.

How do you balance that pain, and Ella and Beckett’s anguish over Ryan’s death, with the growing romance between them?

So that was tough. I am not going to lie. I tried to not overwhelm the reader with so much sadness every single chapter. It is a heavy, heavy book. Because when you have a child with cancer, you can’t compartmentalize it. All you become is that diagnosis and all you become is how hard you’re going to fight for your child. But I think when you’re going through something like that, something that life-altering, I would think as a woman, as a human, you would want to feel closer to someone. You reach your emotional limit, but you have that person who has the ability to ground you and keep you sane and give you a break. And I think Beckett does that for Ella.

What feelings were you trying to evoke in readers?

I hope they feel the gamut of emotions. I hope they feel the highest high of falling in love and discovering the person you’re meant to be with, because I do love writing about love. And I hope that they feel the depth of sadness that’s possible. I think when you witness someone else’s tragedy, when you love that person, even if it’s through a character in a book, it makes you grateful for the things that you have when you close the pages. I hope that when they come out of it, they can look at their kids and know every mom is just doing the best she can. And you cannot keep your kids in a bubble and you cannot protect them from everything, no matter how hard you try.