Maxwell will lead you through the Radiation Scanners and into the Vault itself.
He will bring you into the theater. This is Keith and Gilda's stage. Santiago will be talking about the artistry of the murder. Take a look around the room quickly while the Robobrains and the Mr Handy talk. After that, talk with Maxwell again. This will complete the objective and you will need to start searching for clues.
This part helps start introducing the inhabitants of Vault 118.