Asking for some QuerySet help

models.py

from django.db import models


class ThingManager(models.Manager):
    """A manager for public Thing objects."""

    def get_query_set(self):
        return super(ThingManager, self).get_query_set() # How can I
        # get a QuerySet that returns all Thing objects that have at least
        # one related Piece object whose is_public attr is True?


class Thing(models.Model):
    """A thing."""
    title = models.CharField(max_length=255)

    objects = models.Manager()
    public = ThingManager()


class Piece(models.Model):
    """A piece of a Thing."""
    thing = models.ForeignKey(Thing, related_name='pieces')
    is_public = models.BooleanField()