The fourth season heats up. Picking up from the third season's shocking cliffhanger, the neighborhood immediately ignites with drama. What will Gabrielle do about her new husband? Can newlyweds Susan and Mike find their happy ending? Will the Van De Kamps keep their secret in the family? Can Lynette survive her personal crisis? A controversial new neighbor on Wisteria Lane adds fuel to the fire.
A month has passed on Wisteria Lane since Susan and Gabrielle tied the knot with Mike and Victor. While Lynette is battling with the effects of chemotherapy, Susan finds out she might have menopause. Bree's faked pregnancy comes close to being uncovered and Gabrielle starts an affair with Carlos. After twelve years of absence, Katherine Mayfair (Dana Delany) moves back to Wisteria Lane with her new husband Adam and daughter Dylan, who doesn't seem to remember living there.
After realizing Tom has been letting her win at cards, Lynette kicks him out of her chemotherapy sessions. Katherine suggests a lunch for Lynette to which Bree insists on bringing dessert - her very own lemon meringue pie. Katherine replaces the pie with her own and Bree becomes determined to get the recipe. Julie desperately wants to go to a party but when Mike advises against it Susan forbids Julie from going.
Bree informs the housewives of what she overheard in the Mayfair house. Susan is throwing one of her charade parties, and although reluctant at first, the girls all decide to go when they make sure Katherine is going to be there. Stella makes marijuana-laced brownies to help Lynette through chemotherapy. Susan is uncomfortable having Adam as her gynecologist so she asks Bree for the number of hers. At the party, both Carlos and Katherine get upset when they see Gabrielle and Adam flirting.
Edie is shocked when she receives some news at the gynecologist’s office, an unexpected visitor discovers Bree’s pregnancy is a hoax, and Wisteria Lane welcomes new neighbors who happen to be partners.
Bob & Lee's contemporary water sculpture in their front yard prompts the Wisteria Lane neighborhood association into action. Edie finds out about the affair that Carlos is having with Gaby, and John Rowland, the Solis' former gardener, wants to rekindle his romance with Gaby.
This is the show's first Halloween episode. Edie Britt's biggest fear comes true when Carlos walks out on their relationship. Susan finds Mike's father - who was supposedly dead. Danielle goes into labor right in the middle of the Halloween party...and somebody has to deliver the baby.
Lynette's sisters Lydia and Lucy come to visit. While having dinner with Susan and Mike, Bree and Orson realize they share different views on whether their newborn baby should be circumcised. On a boat, Victor confronts Gaby about her affair with Carlos and she throws him into the ocean. Later, Bree informs Susan that she thinks Mike is addicted to drugs.
A mysterious stalker from Adam's past shows up on Wisteria Lane. Detectives question Gabrielle about Victor's whereabouts. Danielle's baby puts stress on Bree and Orson's marriage. Mike's drug dealer drops by Susan's house. Lynette has a reunion with her long-lost stepfather, Glen (Richard Chamberlain).
An approaching tornado forces the Wisteria Lane residents into basements, cellars and safe rooms.
In the aftermath of the tornado, the residents of Wisteria Lane try to rebuild their lives. Katherine discovers someone may know her secret while Lynette faces the possibility of her family's fate. Meanwhile Mrs. McCliskey has to face the death of one of her dearest friends, Ida.
Two weeks after the tornado, with Mike still in rehab, Mrs. Delfino gets a visit from her cousin Tim (guest star Chris Carmack). Meanwhile, Bree desperately awaits to return to her own house. Gabrielle learns that Carlos' blindness is permanent. Katherine is unable to keep some of her secrets from the women of Wisteria Lane. Finally, a surprise wedding ceremony has its own share of secrets.
Bree and Katherine join forces to plan the Founders' Day Ball. Lynette is surprised when Rick (guest star Jason Gedrick) shows up at the Scavo pizzeria. Gabrielle struggles with the reality of having a blind husband. Mike asks Orson for forgiveness as part of his recovery program, and Orson starts sleepwalking.
Bree and Katherine decide to start a catering business together. Lynette tries to deny her feelings for Rick (guest star Jason Gedrick). Mike learns the truth about his nearly fatal accident. Carlos gets a seeing-eye dog. Dylan meets her estranged father (guest star Gary Cole).
Susan meets her ex-husband, Karl (guest star Richard Burgi) at a Lamaze class, and finds out that he has remarried and is having another child. Lynette learns who was responsible for starting the fire at Rick's restaurant. Bree wants Orson to turn himself in to the police. Gabrielle rents a room to a hip artist, Ellie (guest star Justine Bateman), who has a dark secret. Dylan continues meeting with her father, Wayne (guest star Gary Cole), and Katherine decides to go spy on her.
Adele Delfino (guest star Celia Weston), Susan's mother-in-law, arrives for a visit. Carlos and Gabrielle find out their tenant, Ellie (guest star Justine Bateman), has a dark secret. Lynette has more problems with Kayla. A full scale war erupts between Bree and Edie.
Susan and Mike try to name their son. Mike wants to name him after his deceased grandfather, Maynard. Lynette is arrested for child abuse of Kayla. Bree is being stalked by Orson, and when she meets with Reverend Green (guest star Bill Smitrovich), the reverend tries to hit on her. Gabrielle is still helping the police trying to detain Ellie (guest star Justine Bateman) for dealing drugs. Katherine is visited by her ex-husband, Wayne (guest star Gary Cole), who wants to know why Dylan doesn't have a childhood scar on her arm anymore.
After Katherine announces that she has to leave town, Bree is left responsible for catering Bob and Lee's wedding. Gabrielle finds $118,000 in Ellie's teddy bear. Susan realizes she will soon lose someone she loves. Katherine Mayfair's secrets are finally revealed, and several residents of Wisteria Lane are faced with deadly threats.