Mia Harper was certain about two things in life.

First: peanut butter sandwiches tasted better if they were cut into triangles.

Second: her best friend Leo Parker would always have her back.

At least, she thought so.

It all started on the first Tuesday of fifth grade. The summer had been endless, filled with bike rides down Maple Lane, afternoons at the creek, and late-night marshmallow toasting in Leo’s backyard. They had a rule: No Secrets, No Lies. It was written in blue chalk on Mia’s driveway and circled twice for good luck.

So when Mia spotted Leo whispering to the new boy at recess and then laughing-really laughing-the kind that crinkled the corners of his eyes-something twisted in her stomach.

She tried to shrug it off. “Hey,” she called, jogging over, her braid bouncing against her shoulder.