At the end of Part II, Montag discovers that Beatty has driven him and the other firemen to his (Montag's) house. Montag and the other firemen prepare to burn his house because it has been discovered that there are books in it. Mildred exits the house and speeds away. Beatty remarks to Montag that he will have to burn his own house. The "dreadful surprise" that Montag becomes aware of is that his house is going to be burnt. More significantly, Montag realizes that his roles have reversed. He used to be the one to burn books and houses; now, in this case, he is the one being burnt out. That's why he says to Faber, "This is happening to me." Although Montag had already begun to seriously question his role as a fireman, this was a more significant moment because Mildred is gone and he is literally burning his old life, completely severing himself from that old life:
Montag could not move. A great earthquake had come with fire and levelled the house and Mildred was under there somewhere and his entire life under there and he could not move.