Previously the duty sergeant at the Treacle Mine Road Watch House before the arrival of John Keel demotes him and offers him a future with a greatly-reduced likelihood of personal gain and a greatly-enhanced likelihood of being shouted at. Similar to then-Corporal Quirke in that he has a gnawing hatred of anything better than mediocre as that's all he'll ever be.
Starts off badly with Keel in that he kicks him in the nadgers and throws him in the Tanty, and is relieved beyond measure when Keel doesn't mention it. He can't understand why, however, as - were the roles reversed - the kicker would be in for hell from Knock.
A weaselly little man. Keel thought things that grew on the underside of trees were better coppers than Knock. In his desperation to avoid a shouting-at he throws others to the wolves - dropping Ned Coates in the Cacky in order to get Keel off his own back, for example. It is shown that he gets a substantial income from accepting bribes and demanding "protection money".
He is also a coward - throwing away his weapon and refusing to fight during the events described here.
Knock never uses his first name in public in case of the panic that may set in.