Movie Story : Justin hopes this summer will be the best of his life, but his carefully planned fireworks end in disaster when they blow up the boathouse. Everyone blames him, yet he is certain he is innocent and sets out to prove it. Meanwhile, Maisy's mother Mimsy arrives to spend what she calls her 'last' summer with the family, and Billie crosses paths with a gorgeous tree planter and a climate activist who could ruin her summer too.