It's evening at the cul-de-sac, and the kids are looking at two asteroids through Sean's telescope - one is light-colored and one is dark. Meanwhile, Mitchell's dog Cody seems to have run away because he doesn't like the black sweater Mitchell put on him. The kids learn about how, just like asteroids, some things are easier to see in the dark than others, like a white card is easier to see than Cody's black sweater. This amount of brightness is called "albedo." The kids go to their local beach to surf, but notice that the beach looks completely different from the last time they stood there. There's way more sand, and the ocean is far away! They decide to be detectives and study what has happened, and learn that the larger and smaller beach is caused by the tides - the rising and falling of the ocean.