Bible story
Peter's Denial Explained: Matthew 26 and Caravaggio
On the night of Jesus' arrest, Peter waits in the high priest's courtyard and, when three people say he was with Jesus, denies it three times before the rooster crows, just as Jesus had told him he would. Caravaggio's painting at the Met in New York shows the accusation in three faces and a few pointing fingers.
Updated
The painting

Caravaggio (Michelangelo Merisi)
The Denial of Saint Peter, 1610
Oil on canvas
The Metropolitan Museum of Art, New York
Public domain, CC0 (The Met Open Access) · museum record · credits
Accession 1997.167
Matthew 26:75
Painted in Naples in the last months of the artist's life, according to the Met.
And Peter remembered the word of Jesus, which said unto him, Before the cock crow, thou shalt deny me thrice. And he went out, and wept bitterly.
Matthew 26:75 (KJV)
The story
Earlier that evening Peter promises he will never deny Jesus, even if he has to die with him (Matthew 26:35). After the arrest he follows at a distance into the courtyard of the high priest. A servant girl says he was with Jesus; he denies it. Another says the same at the porch; he denies it with an oath. Bystanders point out that his accent gives him away; he curses and swears he does not know the man. Then the rooster crows.
The context
All four Gospels tell this scene, which is unusual for a story that makes the leading disciple look so bad. Matthew places it right after Jesus' own trial before the council, so the reader sees two hearings side by side: Jesus questioned inside, Peter questioned outside.
Look at the painting
Caravaggio cuts the scene down to three half-length figures in the dark. The Met's essay notes that the soldier's pointing finger and the woman's two raised fingers stand for the three accusations, and so for Peter's three denials. There is no rooster in the picture; the story is all in the hands and faces.
Sources
Verse text from public-domain translations, quoted exactly with the reference. Paintings are named with their museum. Candlelit Bible is independent and not affiliated with any church or museum.