Warning: Full "Game of Thrones" spoilers ahead. This is speculation based on having read "A Storm of Swords" and no advance knowledge of what happens in season 4.
Since HBO has spilt up "A Storm of Swords" into two seasons, season 3 was roughly the first half of George R.R. Martin's novel, we have a pretty good idea of what is going to happen in season 4 although there could still be plenty of surprises.
The "Game of Thrones" series creators, David Benioff and D.B. Weiss, have made plenty of changes, large and small, that have affected the storyline and general structure of the show that differs from what is set up in "A Song of Ice and Fire." Minor changes such as Tyrion not losing his nose as well as the death of Xaro Xhoan Daxos in the HBO series don't alter the overall story too much. Other changes, such as the identity of Ser Barristan Selmy being known by Daenerys and Jorah from the start, affect the overall story line.
In "A Song of Ice and Fire," Barristan's identity is kept a secret and the reveal causes plenty of conflict with Jorah Mormont, as Barristan is from King's Landing and knows Mormont has been sending reports to Varys. Some characters have seemingly been dropped, such as Strong Belwas and Coldhands, and other characters have been changed. Robb Stark's wife in the series, Talisa, is much different than Jeyne Westerling.
So with the knowledge from "A Storm of Swords," what can we expect from "Game of Thrones" season 4?
One thing that will definitely happen will be the Purple Wedding which means the much-maligned Joffrey Lannister will be meeting his end.
Joffrey’s death starts of a chain reaction of events with Cersei accusing Tyrion of the King’s murder. Tyrion is imprisoned and later put on trial and he chooses a trial by combat in order to earn his freedom. Tyrion selects Oberyn Martell, the Red Viper, as his champion and his duel with Ser Gregor Clegane will occur in the eighth episode of “Game of Thrones” season 4, appropriately titled “The Mountain and the Viper.” Unfortunately the Red Viper dies during the battle, as does the Mountain, but Tyrion is freed by his brother Jaime which leads to two shocking deaths.
After escaping his prison cell, Tyrion makes his way to his father’s bedroom and finds Shae, his wife, in his bed. He strangles her and later kills his father, Tywin, before fleeing in a ship. Considering how many events happen in the second half of the novel, this story could be dragged out until next season and could create a dramatic moment early in the fifth season, much like the Purple Wedding.
If they keep Tryion's story line intact for season 4 another possible candidate to get switched for next season could be Sansa Stark. Sansa finally gets an important role to play and soon returns to the Vale with Littlefinger, Petyr Baelish. In "Storm," Petyr marries Sansa's aunt, Lysa, and a kiss between he and Sansa, disguised as Alyana Stone, leads to the death of Lysa. Sansa does not have much to do in "A Feast for Crows" and a lot of the story focuses on politics and Littlefinger. Moving the Vale storyline from season 4 to season 5 adds another shocking death, Lysa getting pushed out of the Moon Door, while making for better TV.
Another death that occurs in "Swords" that may not be included in "Game of Thrones" season 4 may be the death of Balon Greyjoy. Weiss and Benioff have played around with the Greyjoy storyline so it will be interesting to see what happens next. Ahead of the Battle of Castle Black, Ygritte is part of a raiding party but is killed in battle and this death can lead to a pretty emotional moment in the second half of the season.
Last but not least, Sandor Clegane, better known as the Hound, is believed to have died in "Swords" and that is likely to happen in season 4, as it sets up Arya's departure from Westeros.
While it may not be a death, will the resurrection of Catelyn Stark as Lady Stoneheart be revealed in "GoT" season 4?
So, what's the final tally? For season 4 we could see Joffrey, Tywin, Shae, Lysa, the Hound, the Red Viper, Balon, Ygritte and the Brothers of the Night's Watch and Wildlings die during the Battle of Castle Black, although things could change. "Game of Thrones" season 4 premieres on HBO on Sunday at 9 p.m. EDT.