At Death's Door

At Death's Door is an overseer quest and part of the Horsemen of the Post-Apocalypse Part 3 multi-stage questline in Fallout Shelter.

Walkthrough
You will encounter a group of dwellers from Vault 144 who can either be fought or passed without a fight, depending on your dialogue choice. It is possible to gain one bottle of Nuka-Cola Quantum after this conversation.

Then you may work your way through each level, some of the rooms containing more vault dwellers who must be fought, there are also two pairs of radscorpions on the third floor down and one pair on the fourth. You can also skip several rooms and go to the bottom level, to deal with an alpha Deathclaw and then face Death itself, which is a mole rat boss.