What lies does Montag tell in Fahrenheit 451?

Montag, upset by the burning of the older woman with her books, lies about the book he has hidden under his pillow when he stays home sick from work the next day. He covers the book up when Beatty comes to his home:

Montag made sure the book was well hidden behind the pillow.

Further on in the conversation, he lies to Beatty, who asks him if he'll come to work for a later shift.

Montag shut his eyes. "I'll be in later. Maybe."

We know he is lying because he thinks:

I'll never come in again.

When someone comes to the door after Montag has revealed his cache of books to Mildred, he refuses to answer, thinking it is Beatty:

The front door voice called again softly. "Someone here . . ."
"We won't answer." Montag lay back against the wall and then slowly sank to a crouching position and began to nudge the books.

These scenes mark a turning point in the novel. Montag lies because his whole orientation to his world has changed. He can no longer live as he has been. He can no longer burn books. Further, although books are illegal and although he is a firefighter, he has collected and hidden them in his house. He feels he can't let Beatty know, though Beatty must know, especially after Mildred almost reveals the book behind the pillow. Montag lies about coming to work, because he can't let Beatty see how upset and disillusioned he is with burning books.
He tries to tell the truth to Mildred, because he knows at this point he is going to turn against his society. He wants her on his side. However, she betrays him and turns him in, and he becomes a fugitive.