ARROW HUNTS DOWN SHRAPNEL — Oliver must tackle a new threat to the city when bombs start to go off in Starling City. Felicity (Emily Bett Rickards) 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 (guest star Kevin Alejandro) “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 (David Ramsey) races to the plaza to find the bomb before it goes off. Meanwhile, Roy (Colton Haynes) continues to hide his new strength from Thea (Willa Holland) but, after she witnesses his super strength in action at the rally, she demands answers. Laurel’s (Katie Cassidy) suspicions about Sebastian grow stronger once she learns that he grew up with Cyrus Gold, the man who killed Lance’s (Paul Blackthorne) partner. After Donner (guest Star Dylan Bruce) refuses to help her investigate, she turns to Arrow (Stephen Amell) for help.