A Corner of the Universe by Ann M. Martin

Set in the summer of 1960, where 12-year-old Hattie Owen's quiet life is
transformed by the arrival of her previously unknown uncle, Adam, a
young man with mental disabilities.

This book contains: alcohol, anxiety, autism, controversial social commentary, death/grief, depression, derogatory terms (minor),
discrimination, mental illness, profanity (minor), suicide, sexual activities (implied), sexual nudity, and sexual inferences.