On this page of our guide to BioShock Infinite you will find the fourth part of a detailed walkthrough of Chapter 31 - Memorial Gardens. Booker and Elizabeth must return to the gate outside Comstock's house. For the last time, they will fight the boss - the spirit of Lady Comstock. This will allow them to enter the estate.
As soon as you've returned to Lady Comstock's statue her spirit will appear for the last time to challenge you in a duel. The rules of this fight remain the same and this means that you should immobilize Lady Comstock's helpers while focusing the majority of your attacks on the ghost.
If everything goes according to plan everything will return to normal and the gate leading to Comstock home will open. Step through the door located behind the gate to advance to the next chapter.