You can read this scene right here on eNotes. It takes place in Chapter 11. Heathcliff has returned after Catherine has already married Edgar. One day, Nelly sees Heathcliff kissing Isabella, Edgar's sister. Heathcliff tells Catherine that for spite, he is going to marry Isabella because she married Edgar. He does not love Isabella. Nelly tells Edgar, and he storms into the room and tells Heathcliff to get off of his property. Heathcliff refuses to go. Edgar calls for his servants, and Catherine then throws the key to the room (the kitchen) into the fire, locking the three of them in the kitchen. She taunts Edgar, who although he is afraid of Heathcliff (who is bigger and stronger than he is), and Edgar winds up hitting Heathcliff in the throat. This horrifies him and he goes out the back door to find some servants to help him out because there is no way he can fight Heathcliff. Heathcliff decides he probably cannot fight against a few servants PLUS Edgar so he leaves.
You can see exactly what happens at the link below.