The Inquisitor has sent me to the Abbatoir to visit the elder, but I can't get in. I understand the entrances are dark yawning mouths at (1) the end of the main railway and (2) a little ways behind. Whenever I step into them, though, nothing happens and I just get the console message "Trigger is locked" or something.

Did you try the entrance in between the two blocks of the Apiary? I think that's the one you have to use.

Yeah, that was the one. I actually found it out shortly after I posted for help. I'm on day 9 now out and I'm finding it odd that the soldiers are wearing wifebeaters in the midst of a serious infection. Are they vaccinated or something?

No. Most likely, they won't survive this post adn are doomed.

That makes me feel better about stabbing them in the head.