This is the three part finale of Season 1. Most of it is over how Unicron is the rising darkness the prophecy is speaking of and how he is rising. Part 1 is covering how the 'bots are able to figure out what the culprit is. Part 2 is over how Optimus fights the Unicron foot-soldiers (how Megatron describes them) and they eventually team up to defeat Unicron. Part 3 is finalizing how the teamwork goes.