Pride and Prejudice and Zombies takes place in 19th century England where a zombie virus has spread across the country, with the elderly composing a majority of the "stricken", "sorry stricken", "un-dead", "unmentionables", or "zombies". The presence of the zombies cause both subtle and significant differences from the original plot. For example: Messages between houses are sometimes lost when the couriers are captured and eaten; characters openly discuss and judge the zombie-fighting abilities of others and women weigh the pros and cons of carrying a musket.
The beginning of the story introduces Miss Elizabeth Bennet, a young woman living with her four sisters and parents, Mr. and Mrs. Bennet. Mr. Bennet trains his daughters in martial arts and weapons training, molding them into a fearsome zombie-fighting army. Meanwhile, Mrs. Bennet endeavors to obtain wealthy and high status husbands for her daughters. When the wealthy and single Charles Bingley purchases Netherfield Park, a nearby estate, Mrs. Bennet sees an opportunity to achieve her goal and sends her five daughters to a local ball where Mr. Bingley is expected to make an appearance. At the ball, zombies attack the guests and amidst the chaos Mr. Bingley and the eldest Bennet daughter, Jane make a connection. However not all the Bennet daughters are as successful, as friction is presented between Elizabeth and Mr. Bingley's closest friend/ zombie killer, Fitzwilliam Darcy.
As time passes, Mr. Bingley and Jane become closer acquainted, this companionship leaves the Bennet girls confused when Mr. Bingley & Co. suddenly abandon Netherfield Park . When the local militia arrives in town to exhume and destroy dead bodies, Elizabeth becomes friendly with one of the soldiers, George Wickham, who tells Elizabeth that Darcy cheated Wickham out of an inheritance.
Elizabeth's dislike of Darcy intensifies when she learns that Darcy plotted to separate Bingley from her sister Jane. Elizabeth vows to avenge the slight to her family by killing Darcy, and she is afforded that opportunity when he appears unannounced at the cottage where she is visiting her newlywed friend Charlotte (who has been secretly bitten by a zombie and is slowly turning into one herself). Before Elizabeth can fetch her katana and behead him, Darcy surprises her by proposing marriage. The scene culminates in a vicious verbal and physical fight, in which Darcy is wounded. He escapes with his life and writes a long letter to Elizabeth explaining his actions. He separated Jane and Bingley out of fear that Jane had contracted the "mysterious plague" and with regard to the allegedly wronged soldier Wickham, Darcy explains that Wickham had attempted to elope with Darcy's younger sister to take her considerable fortune – this was the "inheritance" that Wickham had claimed. Elizabeth realizes that she has judged Darcy too harshly and is humbled. Darcy realizes that his arrogant nature encourages people to believe the rumors about him and resolves to act more appropriately.
Elizabeth embarks on a trip around the country with her aunt and uncle, fighting zombies along the way. At Pemberley she encounters Darcy, who repels a horde of zombies. Darcy's changed attitude and manners impress Elizabeth and lead her to consider reconciling their relationship; her hopes are dashed when her younger sister Lydia elopes to London with Wickham. The Bennet family fears the worst but receive word that Wickham and Lydia have married, following an "accident" that has rendered Wickham an incontinent quadriplegic. After visiting the Bennets, the couple adjourns to Ireland. Elizabeth discovers that it was Darcy who engineered the union, thus saving the Bennet family from ruin. Meanwhile, Mr. Collins realizes his wife has turned into a zombie, and hangs himself after beheading and burning her.
Darcy and Bingley return to the countryside, and Bingley resumes courting Jane. Elizabeth hopes to renew her relationship with Darcy, but his aunt, the Lady Catherine, interferes, insisting that her daughter Anne is a better match for her nephew. Lady Catherine challenges Elizabeth to a fight to the death, intent on eliminating the competition, but Elizabeth defeats her. Elizabeth spares Catherine's life. Darcy is touched by this gesture and returns to Elizabeth. They cheerfully wipe out a dozen zombies, are married, and begin a long and happy future together, insofar as the ever-present threat of zombie apocalypse permits it. In other words, the writer Jane Austen shows the power of love and happiness to overcome class boundaries and prejudices in the marriage.