Do You Know the Monkey Man? by Dori Hillestad Butler

Samantha is obsessed with finding her dad. He left when she was three, the same year her twin sister drowned on an outing with him. Her mom is remarrying and doesn't like to discuss either Sam's father or her twin. Frustrated by all the secrets, she goes to a psychic. What the psychic tells her is so shocking that she is driven to find out the truth. What Samantha learns on her search changes her life forever.