The Empty Throne is the eighth book in The Saxon Stories.
Æthelred, the ruler of Mercia, is dying, leaving no legitimate heir. The West Saxons want their king, but Uhtred has long supported Æthelflaed, sister to King Edward of Wessex and widow of Æthelred. Widely loved and respected, Æthelflaed has all the makings of a leader—but could Saxon warriors ever accept a woman as their ruler? The stage is set for rivals to fight for the empty throne.
Uhtred is still suffering from the wounds he received in battle. To recover his strength he needs to find the sword that caused the injury, but lost amid the battle’s blood and mud, how could it be traced and who among the Vikings or Saxons might be holding it?
In the end it is one champion, one hero, who will destroy the new Viking threat to Mercia and ultimately decide the fate of England.
The novel's prologue is narrated by Uhtred's son, also named Uhtred, who is fighting a small band of Norsemen in the north of Mercia. The Norsemen are defeated, and Uhtred brings the captured leader and plunder to Æthelflaed, who instructs him to take it to Gloucester, where the Mercian Witan is about to convene.
Æthelred, the Lord of the Mercians and estranged husband of Æthelflaed, has been wounded at the battle of Teotanheale, and is now dying. The Witan, although not explicitly, is convening to decide the fate of the Kingdom after the Lord has died. Eardwulf, whose sister is Æthelred's lover, commands his household warriors. Eardwulf is the leading contender for the Lordship, and Ætheflaed is likely to be sent to a nunnery after Æthelred's death.
The elder Uhtred, who was also seriously wounded in the battle, returns as the narrator. He has been summoned to the Witan. He mistakenly assumes this is so Æthelflaed's enemies can say that someone spoke in her defence when the Witan decides to send her to a nunnery. However, upon the discovery that Æthelhelm, the most powerful Ealdorman in Wessex, is at the meeting he realises this is a ploy to draw him away from Æthelstan, the son of King Edward's first wife. Æthelhelm wishes the boy to be killed so his own grandson can inherit the throne (his own daughter is now married to King Edward).
At the Witan, it is decided that Eardwulf will marry Æthelred's daughter, and inherit the Lordship of Mercia. Uhtred pretends to be dying in order to escape from Gloucester without raising suspicion. He races back to his home where Æthelstan is hidden. After a fight with some of Æthelhelm's troops, Uhtred and his daughter Stiorra murder a priest who had beaten her after she had refused to tell them where Æthelstan was hidden.
Uhtred sends most of his followers, including Æthelstan, to Chester, while he and Stiorra go back to Gloucester to kidnap Æthelred's daughter, in order to prevent her from being married to Eardwulf. After some clever ruses, Uhtred manages to escape with the girl. He then returns to his home being joined by the rest of his followers on the way to Chester. Uhtred then realises he has made a mistake. Even though he made it appear as if he was heading east, Eardwulf and Æthelhelm are sure to realise he is heading to Chester. He takes refuge in an abandoned fort. His priest, Cuthbert, mentions to him an old Biblical tale which implies the sword which inflicted his wound, would also be able to heal it.
Eardwulf surrounds Uhtred at the abandoned fort and demands he surrender Æthelstan and be exiled. Uhtred refuses, and just before he is about to fight Eardwulf, the Lady Æthelflaed arrives and commands Eardwulf return to Gloucester. Æthelred has now died, so it is not clear who has the authority to command the troops. Eardwulf leaves for Gloucester and Uhtred, suspecting an attack, prepares a trap for Eardwulf.
Eardwulf, whose only chance to inherit the Lordship is to marry Æthelred's daughter, decides his only hope is to attack Uhtred and kill the Lady Æthelflaed. Uhtred outwits his opponent and forces Eardwulf to flee with only a handful of troops. Eardwulf's sister, Edith, is captured.
Uhtred returns to Gloucester, and he learns than Eardwulf had returned briefly and stolen Æthelred's wealth. Eardwulf, having attempted to murder Æthelflaed, is now an outlaw. At the Witan, Uhtred manages to convince Mercian nobles to select Æthelflaed as the new leader, much to the anger of Æthelhelm.
Edith becomes Uhtred's lover, and she reveals to him that she knows the location of Ice-Spite. Asser, a monk with a strong animosity towards Uhtred, took the sword after the battle at Teotanheale and has had it taken to Wales. Asser is now dead of old age. Uhtred heads to Wales, but finds the monastery ransacked and the sword stolen by Norsemen. After meeting the king of one of the Welsh kingdoms, Uhtred joins a Welsh army who take revenge on a Norse army who are leaving Wales. The sword Ice-Spite is found, and Edith uses it to drain the pus from Uhtred's body. His pain immediately stops.
Uhtred realises that the exiled Eardwulf has joined the Norse fleet, lead by Sigtryggr, and they are headed to Ceaster to capture the fort from the Saxons. Uhtred rushes to Ceaster. Some of Eardwulf's men have already entered Ceaster and he learns they plan to open the gate for the Norse army. He has them executed and plans a trap of his own.
When the Norse army attacks, they are caught in a small alley in the city and are slaughtered. Sigtryggr himself loses an eye in a fight with Uhtred, and the army retreats. The two armies negotiate that the Norse will be allowed to leave for Irland unhindered, as neither army has enough men for a good victory. As part of the negotiations, Eardwulf is handed over to Uhtred, and he has the boy Æthelstan execute him. Just as Sigtryggr is about to leave, Uhtred discovers Stiorra plans to leave with him. Uhtred, seeing the similarities with himself and Gisela, allows it.