Kate and her younger brother, Alex, build a treehouse in their backyard with help from their parents and grandparents. But, Alex complains that it is too much work, too far, too hot, and too dark, so they use the engineering design process to make it better. Along the way Kate learns STEM topics including simple machines, sound, heat, and electricity while also putting up with her little brother. By the end of the summer, the treehouse is the best treehouse in the world and Kate and Alex can't wait to show it off during a family reunion. Be sure to check out the free, printable activity guide (the web address is included inside the book) so you can learn about simple machines, sound, biomimicry, heat, and electric circuits.