New Delhi, July 24 (ANI): Lucy Lawless is set to join the cast of Marvel's hit superhero-based TV series ' Agents of S.H.I.E.L.D.' The 46-year-old former 'Xena: Warrior Princess' star, who is also an environmental campaigner and Greenpeace ambassador, has been signed for the ABC show's second season, which is due to air in September 2014. The series, which shows the Marvel superheroes fighting world threats post an epic Battle of New York, has not yet revealed Lawless' role or the details on how many episodes she'll appear in.