S2, E10: Oliver must tackle a new threat when bombs start to go off in Starling City. Felicity discovers the person setting them off is Mark Sheffer (guest star Sean Maher), a man who goes by the nickname "Shrapnel." Arrow discovers Shrapnel's next target is Sebastian Blood's "Unity Rally" and tries to talk the alderman out of hosting it, but he refuses. Arrow sets off to stop the bombing, but Shrapnel tricks him and traps him in a bomb-laced antique store where he is unable to move without setting off the device.