I will go tell him of fair Hermia’s flight.
Then to the wood will he tomorrow night
Pursue her. And, for this intelligence
If I have thanks, it is a dear expense.
But herein mean I to enrich my pain,
To have his sight thither and back again.
– William Shakespeare
A Midsummer Night’s Dream, Act 1, Scene 1. Helena decides to tell Demetrius that Hermia and Lysander are planning to run away together the next night. She knows that Demetrius will pursue Hermia and that she is betraying her friend’s trust. But Helena is hoping that Demetrius will be grateful to her for telling him and that she can win back his love.