Here's a link to the text of the play for Act III Scene 5

Juliet wants to cling to her Romeo, but Romeo knows his life is in danger. Both the young lovers are feeling desperate.

This scene occurs after Romeo has slain Juliet's cousin, Tybault, and Romeo has been banished from Verona by the Prince.

Romeo has taken refuge in Friar Lawrence's cell and recives a letter from the grief-striken Julet asking that he come visit her at night.

Romeo climbs a rope and enters Juliet's bedroom; the two spend a passionate night together.

When the scene opens, Juliet does not want the night to be over. Romeo feels he must, as daylight could easily mean his discovery. Therefore, Juliet wants to pretend the night is still with them, and claims that the bird the pair hear is not a lark, a bird of the morn, but the call of a nightingale, who only sings at night (hence the name.)

She tries to convince Romeo of this, saying,

Wilt thou be gone? it is not yet near day:
It was the nightingale, and not the lark,
That pierced the fearful hollow of thine ear;
Nightly she sings on yon pomegranate-tree:
Believe me, love, it was the nightingale.

Romeo does not want to leave, but replies,

No nightingale: look, love, what envious streaks
Do lace the severing clouds in yonder east:
Night's candles are burnt out, and jocund day
Stands tiptoe on the misty mountain tops.
I must be gone and live, or stay and die.