Piper is trying to unclog a sink, when a woman's face appears above the water, asking for help. The sisters orb to a pond and a woman emerges, bearing a large sword. Several demons appear, and one throws a knife, hitting the woman in the back. The sisters fight off the demons and find the sword embedded in a large stone. Paige believes the sword is Excalibur, but Piper is skeptical.
The Dark Knight threatens a mercenary demon, who tells him that the Charmed Ones attacked. He wants "a seat at the table" as his price for hiring more assassins to take out the Charmed Ones. A large round table with a pentagram stands nearby.
Paige's new temporary job is as Phoebe's assistant.
A line of magical beings has walked into the manor and is trying, one by one, to pull the sword from the stone. Piper tries to run them off, and calls for Chris, but Leo responds instead. Leo fetches Phoebe and Paige. Finally, Piper gets angry and grabs the sword -- and it comes out. A man calling himself Mordaunt appears in a vortex and tells Piper she is now the master of Excalibur.
Mordaunt tells the sister what he knows of the Dark Knight and suggests a vanquishing potion. He offers to teach Piper the use of Excalibur. Leo orbs Wyatt "Up There" while Mordaunt produces a sword and begins sparring with Piper.
In the demon's lair they discuss their action. An executioner demon brings in a sack which is revealed to contain a dwarf. They question him about the sword and what he knows. The dwarf informs them that Piper has the sword now and is being trained to use it. The demon demands to know who is training her. The dwarf motions he doesn't know. However, he then punches the executioner demon in his testicles, who lets go of him to grab his balls, the dwarf then escapes zipping out.
Phoebe, Paige and Richard make the vanquishing potion at Richard's place.
The Dark Knight and three demons shimmer into the manor. Piper fights the Dark Knight while Mordaunt takes on the three underlings.
At Richard's place, Phoebe and Paige are continuing with the potion. Phoebe is about to add black poppy when Richard yells "NO!" and, through telekinesis, pulls Phoebe away. Phoebe has been mistrustful of Richard, but he then tosses the black poppy in, causing an explosion. Richard says, "Don't ever mix wraith essence and black poppy". He, Phoebe and Paige realize that Mordaunt wants them dead.
More demons attack, but Piper and Mordaunt kill the last of them. Paige and Phoebe orb in and try to warn Piper, but she and Mordaunt fade away -- to the Round Table with the pentagram. Mordaunt promises Piper great power, and kisses her. He reaches for Excalibur but it evades his grasp. Piper and Mordaunt have gathered several demons to the round table. They offer a loyalty oath and the demons all explode, their powers transferred to Mordaunt. Mordaunt claims Excalibur from Piper. He tells Piper that Wyatt was the true owner of Excalibur, and impales Piper with Excalibur.
As Leo heals Piper, Mordaunt shimmers into the manor and tries to stab Wyatt with Excalibur -- but it's only a teddy bear. Paige orbs back in with Wyatt, and Leo with Piper and Phoebe. Wyatt orbs Excalibur to himself and he hurls it back into Mordaunt, vanquishing him.
Piper puts Excalibur back into the stone and Paige orbs it to the attic until Wyatt is old enough to use it. Leo also fixes all the things wrong in the house for Piper, leaving her more time to spend with Wyatt.