Complex sentence: On the way back to Earth, Titus detains Jupiter and Caine, to whom he reveals his plan to marry and then kill Jupiter and claim Earth before throwing Caine into the void; but Caine survives and saves Jupiter at the altar.
Split into simpler sentences: On the way back to Earth, Titus detains Jupiter and Caine. He reveals his plan to marry and then kill Jupiter and claim Earth before throwing Caine into the void, but Caine survives and saves Jupiter at the altar.