"Opening Doors" is the 84th episode of the ABC television series, Desperate Housewives. It is the fourteenth episode of the show's fourth season and aired on May 4 2008 in the United States. The title comes from a Stephen Sondheim song from his musical Merrily We Roll Along
Susan reconnects with ex-husband Karl (Richard Burgi) while she is in Lamaze pregnancy class. She and Julie met Karl and his present wife Marissa at the class. Karl says offensive statements to Susan, like she has aged, gained weight and so on and brags about Marissa being a law professor. Furious, Susan brings Mike to the next class dressed in a suit. Mike lied about him now hiring people to do plumbing and having a great social life, but then he goes on and tells Karl and Marissa the reason he missed the previous class: He was getting the 30-day chip which signifies he has successfully been through 30 days without drugs. Susan is unhappy that Mike told them about his drug addiction, but Mike told her that he should be honest about who he is and he does not care what Karl thinks. The next class Karl told her that Mike tries to be honest as he loves her, unlike Karl who was always dishonest to her.
Gabrielle rents out her guest room to earn some money, and an art student named Ellie responded to the classified and moves in with the Solis's. When Gabrielle wants to borrow a nail file from Ellie, she saw a man in Ellie's room (who was different looking than a man she saw earlier in the day), which made Gabrielle feel awkward. She then noticed Ellie counting some money after the man left, and made a conclusion that Ellie is a prostitute. Gabrielle then asks Bob to act as someone who wants to have sex with Ellie to catch her in the act. Bob seemed reluctant about the plan, but his partner Lee voluntarily wants to play the role. However, the plan turns sour when Ellie slapped and kicked Lee. When Gabrielle apologized and confessed her intentions, Ellie told Gabrielle that she is running a tattoo parlor in the room so that she can earn some money to open her own shop. Ellie forgives Gabrielle and agrees to stay longer. It turns out that Ellie is actually a drug dealer and there are significant amounts of drugs in her drawer.
The twins, Preston and Porter are punished to do chores for burning Rick's restaurant. Tom suggested to take the boys to therapy, which Lynette is against. One morning, Lynette overheard the twin's conversation. They hinted that it was actually someone else's idea of setting the fire, and then at Lynette's command confessed that this "someone else" was Kayla. She then confronts Kayla about the incident. Kayla says that the boys wanted to hurt Rick with dynamite. Kayla told Lynette that she was merely joking when she told them that everyone has matches instead of dynamite. Lynette is shocked that Kayla was incredibly calm and showed no remorse, so she took Kayla to the therapist without Tom's knowledge. In the waiting room, Kayla suggested to talk to the police as well, which Lynette thinks is unnecessary. Tom argues with Lynette subsequently after that while Kayla crept outside the house with an umbrella. She manages to convince the twins that she had just jumped off from the roof (in reality she jumped off from the porch), and Preston broke his arm while he attempted what Kayla told him. Lynette noticed Kayla's cold stares as Tom and herself took Preston to the hospital.
Dylan claims that she is dating a boy in school, which Katherine only heard about but had not seen yet, in reality she is meeting her father, Wayne for dinner every night. One night, Wayne would come clean to Katherine and tell her how sorry he is. Katherine discovers their secret meeting when she decided to spy on Dylan one night. Dylan then admits that she is lying about a boy she's seeing and she was seeing her father and then invited him to the house. Wayne told Katherine that he has changed after 12 years, and she told him she is no longer afraid of him anymore. When Wayne left the house, Katherine sighed in relief, and it is revealed that she hid a revolver in the drawer.