Death and Friendship

Act 3, scene 1

Mercutio
I am hurt.
A plague o' both your houses! I am sped.
Is he gone and hath nothing.

Ask for me tomorrow, and you shall find me a grave man.

Benvolio
Romeo get out of here. The citizens are around, and Tybalt is dead. Don't stand there shocked.The Prince will give you the death penalty if you get caught. So get out of here!

Task
Explain what has happened to make these two men speak so urgently.
Why was it important for the play that Mercutio die.... what were the consequences for both families?