In the worst letter ever, Griffin tells Kemp that he is taking charge: "Port Burdock is no longer under the Queen, tell your Colonel of Police, and the rest of them; it is under me—the Terror! This is day one of year one of the new epoch—the Epoch of the Invisible Man. I am Invisible Man the First" (27.2).
The letter also says that Griffin will kill Kemp that day. No big deal.
What's even better is that Griffin sent that letter without a stamp, so Kemp had to pay for it upon delivery. As we said, worst letter ever.
Kemp has his housekeeper lock up all the windows and gets his revolver ready. He writes a note for Adye, saying that Kemp will act as bait to catch Griffin.
Adye shows up later, saying that Griffin grabbed the note from Kemp's servant. So now Griffin knows that Kemp wants to set a trap. Bummer.
Then Griffin does what he does best: he breaks some windows. But there's no way for him to get into Kemp's house because they've anticipated his arrival. This is the siege of Kemp's house. (A "siege" is an old term for when one army surrounds a castle or fort. The army inside can't get out, but the army outside can't get in. Eventually everyone gets bored and hungry.)
Adye borrows Kemp's gun and tries to go for help, but Griffin trips him up and grabs the gun.
At first, Adye refuses to help Griffin, but he changes his mind when he realizes "that life was very sweet" (27.52).
The narrator switches point-of-view here, and goes from Adye to Kemp, who is watching all this from an upstairs window. Suddenly, he sees Adye attack Griffin and get shot. It sure looks like Adye is dead, but we're not sure.
Kemp's housemaid is coming up the hill with two policemen. At the same time, Griffin has found an axe and is using it to break through the shutters over a window. This is what we call suspense.
Luckily for Kemp, the police get there in time, and he gives them some fireplace pokers to use as clubs. So it's pokers vs. axe-and-revolver, though Griffin isn't a great shot.
Griffin knocks out one of the cops, but the other cop hurts Griffin (by aiming near the axe). There's a snapping sound, so maybe his arm gets broken. Griffin drops his weapons and runs away.
But when the cops look around, they find that Kemp and his housemaid have also run away. That probably doesn't make them feel too great about the guy they just saved.