The Favor by Blaire Edens

Single mom Anna Bishop doesn't want help from anyone, but she does need a superhero for the birthday party she's has planned for her seven-year-old. Luckily, her best friend's brother agrees to suit up and play the role.
When architect Clark Wainwright agrees to do his sister a favor, he never expects to end up in a pair of tights...not to mention the tight spot he ends up in when he creates trouble for his sister's best friend. Clark is a fixer, and he'll do whatever it takes to fix the problem he causes for Anna and help her keep her son...whatever it takes...even of it means proposing.
Anna could do with a little rescuing...but it just might be Clark who gets saved in the end.