Sean Maher (Firefly) is set to guest star as the evil Mark Scheffer, who is known as DC Comics supervillain Shrapnel, a serial bomber who places Starling City in a grip of terror and threatens the life of Sebastian Blood (Kevin Alejandro).
Sean's character will first appear in episode 10 (which is most likely to air late December/Early January).
His appearance marks yet another lFirefly alum to join the series, with Summer Glau previously cast as Isabel Rochev on the show.
Source: The Hollywood Reporter
What new evil will Mark offer to Starling City? And are you happy to see more Firefly members on the show?