Who's Herbert? Arthur meets him in the dungeon under the Cheese Hall, at first seeing him through the divide between their cells as a man in a mask. As they talk, Herbert describes his iron socks and his walloper, and while the walloper is a giant hammer he made from his prison bed, the iron socks are to keep him stuck to a magnet that Snatcher's goons turn on when he's causing a ruckus. Yikes.
Magnets to the wind, the whole walloper thing does come in handy. Herbert smashes the railings keeping Grandfather, Willbury, and the rest prisoner in the Cheese Hall, and then he smashes through the wall to get them all out of there. Forget Hulk Smash—it's Herbert Smash in this book.
The weird thing, though, is that Herbert has no idea why he's locked up. When Arthur questions him, he says stuff like: "'Me? Can't remember. Something to do with me and hmmm […] Can't rightly say'" (32.37-39). We meant it when we said the guy doesn't have a clue.
It's only when Arthur calls up Grandfather that we learn the truth: Herbert was Grandfather's childhood buddy. They were both unfortunate enough to be at the scene of a crime Snatcher committed, and Snatcher locked up Herbert so that his false accusation against Grandfather wouldn't be challenged.
Herbert slowly puts together the pieces with Grandfather's help, and that's when he realizes the full extent of his situation: "'They must have had some more Oil of Brussels and smothered me with it. That's why me memory is so bad! […] And I guess we've both been prisoners of sorts ever since…'" (39.58). Yes, Herbert, that's the short version of it; Snatcher basically ruined your memory and your life a number of years ago.
Herbert helps save the day by smashing things, and then he gets to look forward to a nice life outside the Cheese Hall once Willbury clears his name in court. Plus he gets to renew his friendship with Grandfather after all these years, too. Not bad, eh? And we'd say Herbert deserves it.