Complex sentence: After landing on Persephone, Simon, looking for a ship to take him and River off-planet, chooses the ship "Serenity", which had just docked at the Eavesdown Docks.
Split into simpler sentences: After landing on Persephone, Simon, looks for a ship to take him and River off-planet. He chooses "Serenity", which has just arrived at the Eavesdown Docks.