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 Sheffner (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. While Felicity helps Oliver, Diggle races to the plaza to find the bomb before it goes off. Meanwhile, Roy continues to hide his new strength from Thea but, after she witnesses his super strength in action at the rally, she demands answers. Laurel's suspicions about Sebastian grow stronger once she learns that he grew up with Cyrus Gold, the man who killed her father's partner. But when Donner refuses to help her investigate, she turns to Arrow for help.