Renfrew spends his Saturday morning putting up new shelving to store the canned food Marjorie has been creating to get the family by.
He makes the shelves perfectly level, but the house has been tilted with age; Marjorie complains they look off.
Renfrew takes his son, Johnny, to an organized mercury hunt through the sewers.
On the way, they stop by Renfrew's office at the Cav and bike past Institute for Astronomy.
At the Institute, they meet Mr. Frost, who remembers Johnny coming to Observer's Night. They learn the old curator has been living in the old building since he has nowhere to go, and it was recently broken into by thieves, who took their share of the collector's items.
Mr. Frost managed to save a late edition of Kepler.
At the mercury hunt, Renfrew and Johnny manage to find some mercury and also discover a squatter's hideout.
Renfrew has one of those dad-realizing-his-boy-is-growing-up moments.
Back home, Marjorie again points out that the shelves don't look square, and Renfrew comes to see things from her perspective.
He made the shelves perfectly, mathematically level, and it is the house that has warped with time, yet it is the shelves that seem to tilt.