I loved this trailer. They did everything right in my opinion. They keep giving us the same content in the trailers mainly but give it a spin so as to not spoil anything. They introduce just a little bit more each time. Here are some notable details I picked up in the trailer: Halsey has 2 arms in the beginning indicating that this is a flashback. Toa from Halo Canon has hypothesized that this could possibly be her entering her lab in Castle Base on Reach. There might be some tie to Reach here or this could just be for backstory on Halsey's relationship with ONI. She's talking to Locke which means that this monologue is probably taking place after the first mission when she's captured by Osiris and brought back to Infinity. "Once this is over, after all we have done, they will order you to kill us both." It seems that this mission may not be all that Locke thinks it is. Locke's mission is to bring the Chief back but Halsey is certain that once he does, he will be given the order to terminate Halsey and the Chief. "I tried to warn you this was happening." Halsey says this to Palmer indicating that there was some kind of communication on the subject beforehand. This is obviously in current-time because she's on Infinity with Palmer and missing her arm. Locke is holding his BR to John telling him to stand down. Here, it's shown that Chief doesn't have a crack in his visor yet. If we recall from the trailer released in theaters, Locke and Chief have a brawl here where Chief delivers quite a headbutt to Locke. Before entering the portal, Chief has that crack in his visor we see later on indicating Chief may have won this bout which is why he can walk through that portal with no opposition. It appears you will be fighting alongside the Arbiter in gameplay as Fireteam Osiris because you can see Locke walking up the stairs to find the Arbiter hip tossing a Zealot like a badass. There will be a fight with the Warden either before or after the little dialogue we have with him shown in the Believe Trailer. John gets slashed up. 2:07 if you pause at the right moment you see the Arbiter slashing an opposing Elite with an orange colored Prophet's Bane. it's beautiful. Lastly, this was a theory from a member on Halo Archive, but the fact that it says "experience the beginning of the greatest hunt in gaming history" may indicate that this hunt, whether it be for John or just for the truth, could span over more than just Halo 5: Guardians.