Complex sentence: In the episode, "There's No Place Like Home" after visited by Locke, Walt visits Hurley at the Santa Rosa Mental Institution with his grandmother, under the assumption that his father is still alive and living on the island.
Split into simpler sentences: In the episode, "There's No Place Like Home" after visited by Locke, Walt visits Hurley at the Santa Rosa Mental Institution with his grandmother. Walt is under the assumption that his father is still alive and living on the island.