Note: Some editions of the play cut this scene altogether. So, don't trip if your book doesn't have it.
Somewhere in England, York gives Sir Michael a letter to take to the Lord Marshall, Thomas Mowbray (an important leader of the rebels in Henry IV Part 2).
York discusses the battle that's about to go down at Shrewsbury. He's heard that Northumberland has phoned in sick and Glendower's troops haven't been put together yet. He fears the king's troops will overpower the rebel forces.
York also says that Mortimer isn't there and the king has amassed an impressive army of men.
York worries that after the king defeats the rebels at Shrewsbury, he's coming for him and the other remaining rebels. (He's right. Stay tuned for Act 5, Scene 5.)