After Griffin makes sure the bedroom is secure and after Kemp promises not to turn him in, Griffin goes to sleep.
Kemp can't sleep right now. For one thing, he's worried briefly about his sanity (was that really an invisible Griffin?). For another thing, Griffin took his bedroom.
Instead, Kemp spends some time reading the newspapers from that day. The top news story is about a dangerous invisible man. Kemp remembers all the way back to Chapter 16 and he wonders why Griffin was chasing that tramp. That didn't look like innocent fun.
Kemp worries that Griffin may become more unstable and dangerous. He hesitates, but eventually decides to write a note to Colonel Adye. (Perhaps it's a love letter? We won't find out until later.)
Then he hears Griffin wake up. As usual, Griffin starts his day off by tossing some furniture around. It's good exercise – like yoga for mad scientists.