Lois' Sister is the thirteenth episode of season five of Malcolm in the Middle.
Susan visits and Lois finds out that Susan would die unless she would take Lois's kidney. This is something she would rather prefer, still blaming Lois for stealing Hal away from her. Malcolm and Reese take their new '69 Mustang out for a party. Francis is held hostage by a group of Girl Scouts.
Lois' younger sister, Susan, comes for a visit with gifts for the boys, but Lois is suspicious and this causes a fight between them. Hal later bans the gifts Susan gave them, but won't tell the boys why, among with Hal secretly taking out the engine for the car.
Meanwhile to make extra money, Francis volunteers himself to be a guide for a group of Girl Scouts with their leader, Megan, across the desert for a weekend. As they're preparing to leave, she unexpectedly gets a call from her doctor revealing her deadbeat brother's actions and of which she had forbidden the use of her frozen eggs to him. Megan is angered by his actions and tells the group she must leave for town at once. The girls are bummed as she explains that she has to stop her brother from using her frozen eggs in an attempt to get his sleazy, infertile girlfriend pregnant via in-vitro insemination. Megan had promised her ex-husband(whom she divorced amicably) and his gay lover that she would surrogate for them after the Girl Scouts' weekend trip to the desert and thanks to her brother, she has to return to clean up the mess. Francis volunteers to help cover for her by leading the group for the desert trip. Megan thanks him for helping her out and leaves in the van. Francis soon finds himself over his head when the scouts have a different opinion of fun. He is driven insane by the group of girls.
Back at the house, Susan tells the boys why Lois had barred them from the generous gifts she gave them. She claims her belief that the reason their mother acts like this is because she is jealous of her and has to be a control freak to keep herself ahead. Susan mentions it because she was higher class and talented, who can amount to anything. Whereas, everyone saw Lois as a pushy control freak who was untalented and classless. Thus, it was why no one liked being around her. Susan reveals that the only person who was good for Lois was her ex-boyfriend from their time in college, Matt, and she made her biggest mistake in letting him go. Susan also mentions that she used to date Hal and both his family along with Victor and Ida wanted them to marry years ago. She reveals she is still angry with Lois for stealing Hal away from her and the family she should've had with him that led to her unmarried status. Lois acknowledges the truth, but refused to apologize for her actions because she loves Hal more than Susan ever will. She states that nothing their parents and Hal's family can do to change that, which leads to another fight.
Later on, Dewey takes back his cotton candy machine, but goes overboard with his creations until he gets trapped within it. He would eventually eat his way out of his own trap.
Lois gets a call from a doctor and discovers that Susan is dying from kidney cancer. She never told them this as a result due to the friction between the sisters and their families. Despite Hal's warning not to prolong her life, Lois secretly goes to Susan's doctor to get herself tested and is found to be a match.
Malcolm and Reese takes back the car from the garage. Reese has the Mustang towed onto a cliff, then leads it down for a big speed and they drive to a keg party, but as the police arrive, they block other people's cars and all are arrested(presumably explained why the kids stopped inviting Reese and Malcolm to their gathering later on).
Francis finally regains control by pulling a Lois on them. He and the lead girl agrees not to mention this to Megan as long as he leads them to the desert with her. When Megan returns after having dealt with her brother and notices the Girl Scouts have misbehaved, she prepares to punish them. Francis covers for them by mentioning, it was his fault for having not asked them what they wanted to do and thus resulted in them misbehaving themselves. Megan is impressed with his maturity and they do the tour in the desert properly.
Susan goes to the hospital to discovered what Lois has done and is angry with her for going with the surgery. She explains that it's a pathetic attempt on Lois' part to try and stay ahead of her. The doctor tries to convince Susan to take the kidney, but it falls on deaf ears. Hal confronts Lois for being that stupid to try and save her life by giving up one of her kidneys. He points out that he knows Susan too well that she'd refuse and that Lois should've cut her losses. She refuses, pointing out that Susan is still her sister. Hal still disagrees with and reminds Lois how much Susan hates her. Overhearing this, she agrees with his assessment. Susan announces she'd rather die than to accept a kidney from Lois who had willingly stolen the love of her life away from her and made everyone's life a living hell. Lois tells Susan good luck because Victor is in the afterlife. She tells Lois off that she'd rather take her chances with their dad than accept the kidney from her. Susan mentions that unlike him, Lois never loved her enough to respect her wishes for death and thinks she's just doing this intentionally to prolong her suffering. She still demands that Lois honors her request for death and let her join Victor in the afterlife. Lois maintains her stance in refusing and asks Susan to take the kidney from her because despite their past problems, she does love her. Susan begrudgingly takes the kidney, but still prefers death.
The boys each learned a lesson from all this. Reese and Malcolm being careful in not driving a car without an engine and Dewey cutting back on sweets.
- Jane Kaczmerek as Lois
- Bryan Cranston as Hal
- Christopher Kennedy Masterson as Francis
- Justin Berfield as Reese
- Erik Per Sullivan as Dewey
- Frankie Muniz as Malcolm
- Jonny Acker as Ira Prescott
- Laurie Metcalf as Susan
- Abigail Mavity as Meagan
- Kevin Cooney as Dr. Dumont
- Lyndsy Fonseca as Olivia
- Heather McPhaul as Trish
- Jasmine Di Angelo as Brittany
- Kate Miner as Katie(as Kate Lang Johnson)
- Josh Jacobson as Matt
- Hayley Erin as Buttercup #1
- Tianna Danielle Kenney as Buttercup #2
- Alyssa Monka as Buttercup #3
- Montana Tsai as Buttercup #4
- Gracie Markland as Buttercup #5
- Chanel Gaines as Buttercup #6
- Barbara Scolaro as Buttercup #7(uncredited)
- Carrie Cline as Cute Cheerleader(uncredited, as Carrie "CeCe" Cline)
- This episode is the reason why the kids at Malcolm and Reese's school stop inviting the two to a later get together for Ditch Day in Chad's Sleepover
- The spot where Reese had the Mustang towed to and where he and Malcolm start rolling downhill can be found here.
In the middle of the episode, when Lois is confronting her sister for claiming to be an only child, the baby Susan is stroking can clearly be seen to be a doll.
Much like the episodes Lois' Makeover and Lois' Birthday, the name of this episode contains a grammatical error. For a possessive apostrophe to be not be followed by an "s," the subject must be a plural noun that already ends with an "s." Since "Lois" is a single Proper Noun, it requires an additional "s." "Lois's Sister" would be grammatically correct.
"You see this scar? When I was six, and you were four, dad said we couldn't have dessert, because we were bad. And you dumped his ice cream on his head and said 'well neither do you!' And I laughed so hard I hit my head on the table."