After the ensemble kerfuffle of his last outing, Cap’n Am must contend with a fracturing S.H.I.E.L.D., conflicting loyalties and the louring presence of a pallid, metal-armed assassin type harshing his 21st-century buzz. There to bolster his brawn are Black Widow (playing second banana – again), gadgetry of varying daftness and some fun cameos. Perhaps the…