The Polis mission is essentially an interactive cut scene. The only important item is a single Diary Page, and this unmissable achievement at the end.
Check out the video below for a full playthrough of the game showing all collectibles, miscellaneous achievements like this one, and the Moral Points I obtained (I skipped a lot of them) in order to get the Redemption achievement. The Polis mission starts at timestamp
2:02:43.