Teammate A.I. is terrible during the single-player campaign. In theory, your Librarian is flanked by a couple of certified bad asses, both decked out in heavy armour and even heavier weaponry. In practice, they’re borderline useless. Apparently the burden of firing any direction but straight ahead is too much for them, and they’ll happily wander into your line of fire or stop in an entryway you’re trying to seal just for good measure.