Back from Baltimore, House jaunts into the hospital. Cuddy and Wilson are immediately suspicious about his good mood. House happily admits to Wilson that he kissed Stacy on the trip. Wilson barges into Stacy's office demanding to know what happened in Baltimore. He angrily reminds her that the last time she left House, Wilson was left picking up the pieces. He has done so for five years.
Margo Dalton, a 30-something, do-everything mother, notices her arm twitching. This causes her to accidentally plow her car through her garage door. Her husband Ted rushes out to find Margo's body flailing wildly.
The team reviews what they already know. Margo has had a year-long fertility regimen, which explains the excess estrogen in her system. House orders a pregnancy test and an MRI. He wants to know if the problem is in her head or in her uterus.
Margo's MRI comes back clear. The problem isn't neurological or pregnancy-related. They will run a genetic test for Huntington's and put her on Tamoxifen to counteract the estrogen. Margo is upset that this will undo all of her fertility treatments.
Foreman reports to House that, with hypervigilance and sudden irritability, the patient is now defining Huntington's. Yet House thinks the progression is too fast to be Huntington's. Chase notes that Huntington's patients don't advance to psychosis so quickly. Suddenly, Foreman gets a page and they rush to Margo's room where she is having a psychotic episode. This is contrary to Chase's statement.
Margo tests positive for Huntington's and the team is stumped. House starts thinking about Margo's packed daily schedule and he wonders whether cocaine might be a possibility. He sends Cameron and Foreman to search Margo's house. House then heads off to discuss Stacy with Wilson. He wants to know what Wilson said to her.
Foreman and Cameron find a bottle of Ritalin in Margo's car. House connects the dots: Ritalin combined with estrogen explains the flailing and psychosis. She was clean when she entered the hospital, which caused all of the symptoms to die out. House wants to discharge her, but Foreman warns that they will need a confirmation before they can do that.
Ted and his daughter, Stella, sit besides Margo's bed. House starts talking to the little girl. Margo tries to deny using drugs, but House waves the tox screen results in front of the family. She admits to Ted that she was taking Stella's Ritalin. Then she sees that House was only waving a cafeteria menu around.
Later that night, House drops by Stacy's office. She announces that she's moving back home now that her husband Mark is improving. House says that he loves her and doesn't want her to leave.
Margo is walking out of the hospital with Ted when she stops. A blood cot moves into her brain and becomes lodged. Margo collapses to the ground.
Cameron calls House at home with news of Margo's stroke. House rolls over in bed and tells Stacy that he has to go back to the hospital. The doctors wait for House because they saw him leave earlier with Stacy. Cameron reports to House that the Ritalin didn't cause the stroke. House wonders if maybe the Ritalin and the fertility meds were competing. Cameron realizes that fertility treatments can cause endometrial cancer, which Chase mentions could cause a stroke. House orders an MRI of Margo's uterus.
While the team runs the test, Stacy and House meet on the hospital roof. She hasn't told Mark, but she doesn't know what she is going to do. House wants her to decide between him and Mark.
The test results come back negative for cancer. House insists that it is in there, and he demands that they find it. Before Chase can start a biopsy, Margo's BP drops and blood starts to pour from her vagina. Chase uses an ultrasound wand to find the internal bleeding as Margo passes out. Chase lets Ted know that the bleeding stemmed from the liver and flowed through the Fallopian tubes. Margo does have a tumor in her liver but more tests will determine if it's cancer.
Foreman tells House that they can't biopsy Margo's tumor because it is vascular. Before House can react, Mark interrupts. He wants to know why Stacy won't talk to him. House just walks off but Mark follows. House tries walking up the stairs to get away, but Mark drags himself out of his wheelchair and pulls himself up the stairs. House calmly walks away.
Back in the office, House is confused by the liver tumor because the symptoms don't add up. House asks the team what they know about Margo as a woman. Why does she want another child in her busy life? The Ritalin caused the psychosis, but only one other thing explains the clot and the tumor: birth control pills.
House wakes up Margo and asks if she wants a hysterectomy. He accuses her of sneaking birth control because she doesn't want a baby even though Ted does. She denies it. House tells Margo that her tumor is benign and will disappear if she goes off birth control. He wants to cancel the surgery and she can explain to her husband why. Margo again denies that she's on the Pill.
House tells Cuddy that he's calling off Margo's surgery but Cuddy won't have it because the surgery is underway. The tumor is benign. Foreman later informs Ted and Margo about the results and, without saying too much, says the symptoms will disappear. When Ted leaves the room, Margo asks Foreman to tell her husband that she can't undergo more fertility treatments. Foreman refuses to lie, so she asks for birth control that won't cause her to be sick. Foreman warns her that the continued lies will eventually kill her.
That night, Stacy slips into House's office. She is planning to tell Mark tonight about their tryst. She wants to stay with House. He advises her not to do it. House will never change his ways, but Mark is willing to do whatever it takes to make their relationship work. House won't and cannot make her happy. House walks out, leaving Stacy in tears.