LOST - "One of Us" - Jack's joyous reunion with his fellow survivors is cut short when they realize that accompanying him is one of "The Others," and Claire is stricken by a mysterious, life-threatening illness, on "Lost," WEDNESDAY, APRIL 11 (10:00-11:00 p.m., ET), on the ABC Television Network. (ABC/MARIO PEREZ) ELIZABETH MITCHELL, EMILIE DE RAVIN, MATTHEW FOX