It’s an idea that I’ve been throwing around for a while: that Locke is on a mission to kill Master Chief. Halsey is working with the covenant now, and Chief may be looking for her among others like the Didact and Cortana; if he isn’t, the Chief and Halsey are still very close and Halsey “joining” (no doubt they don’t consider her a “member”) the covenant would definitely make Master Chief a liability especially now that he’s gone AWOL. To avoid the risk, ONI could very well have tasked Locke with the assassination of the Chief in the same way that they ordered the assassination of Dr. Halsey.
I don’t remember the name of the director of ONI and I don’t feel like looking it up but what I do know is that she used to be a Spartan (I believe she was a failed subject of the physical enhancements). This makes the fact that she ordered Halsey dead intriguing. Regardless of whether or not she was friends with Chief, my theory is in no way ruled out since she was so happily eager to kill Halsey. Maybe she has some resentment for the Chief; for being better than her, for making it through augmentation in one piece, jealously…
If my theory is indeed correct, Locke is extremely arrogant for thinking he can trick the Arbiter to helping him. From what we know from the games and the terminals, Thel is as powerful as the Chief and as smart as Captain Keys. And he would know when someone is lying to him.
Finally, this might not sound like the Locke we saw in Nightfall. It seems to me that the events at Nightfall made a turning point in Locke’s life and changed his core ideology. He might not be as righteous and noble as he was when we last saw him. He’s seen what people can become when they are on the edge of death: he’s seen human nature at its ugliest point. He may no longer care about acting honorably but more by whatever means necessary. But if there’s anything we know about our dear Arbiter, it’s that he does value honor, and he would never betray his friend for the interests of his enemy.
I think Locke is going to get crushed by the Arbiter by the end of Halo 5 campaign
