They build some weird toy together, Uncle Barry calls Agatha to come with him, they're moving again. Agatha and Gil are dissapointed, and Agatha decides that, since she keeps having to leave stuff behind with all the moves, it's best that Gil keep it.

Years later, possibly while moping over Agatha's "death", he comes across a box of his childhood things. Among them is the weird toy, and he remembers . . . then angsts out even more.

I need to go write this.