I'll try, but there's a bit of a problem: we may have different editions, and so what's on pages 40-80 in my version might not be the same as what's pages 40-80 of your version.
That said, in my version, the firemen arrive at a house that's been reported for sheltering books on page 38. They burst into the house and soak things with kerosene, but the woman who owns the books won't leave, and in fact, she sets her house on fire with herself in it. However, Montag steals one book from the house.
This upsets Montag (and his world). When he goes home, he cries over his wife. The next morning, Mildred (his wife) tells him Clarisse's family moved and that she thinks the girl is dead.
The next morning, Montag plays sick and stays home from work. Beatty comes to visit him and reveals that he knows that firemen always steal a book at some point, and that Montag can burn the book on his own and come back to work without penalty. Beatty also explains how their society moved to the state it is in.
After he leaves, Montag shares the books he's saved from different fires with his wife. This incriminates her too, and puts their entire life at risk. When this section ends, Montag is reading Gulliver's Travels to his wife, who insists it makes no sense.