S1·E9 A Thing or Two About Loyalty

Lambert, a friend of Sir Guy of Gisborne and castle scientist, realises that lives could be at risk if his latest invention were to fall into the Sheriffs hands. When Lambert won't make more of the invention, an "explosive" black powder, he is put into the dungeons by the furious Sheriff. Much volunteers to get himself arrested so he can help Lambert from within, but will he get more then he has bargained for?