Neil Patrick Harris (How I Met Your Mother) stars as Billy, A.K.A. Dr. Horrible, a budding supervillain whose plans for world domination continually go awry. His two goals: getting accepted into the Evil League of Evil, and working up the guts to speak to his laundromat crush Penny, played by Felicia Day (The Guild). The only thing standing in his way is Captain Hammer, Billy's superhero archnemesis played by Nathan Fillion (Firefly). With one big score, Billy could get into the E.L.E. and earn the respect of Penny, but only if he can keep her away from the dashing Captain ...