on the boathouse between terror lake and springfield, sideshow bob starts singing 'and its clearly to his credit that he is an englishman he remains an english...' he stops when he realizes 'wait did you only ask me to sing to forestall your gruesome end?' bart smugly admits 'guilty as charged.' but before bob can deal the coup de grace, lisa manages to get untied thanks to snowball 2 and open the door. She yells 'bart! look out!" and dives between him and bob, bart hears the ripping of her dress against bobs sword followed by lisas blood curdling scream followed by her blood poka dotting his face like chicken pox. He rushes to her side asking 'lisa! why did you do that? why did you save me?' lisa through dying coughs replies '*cough cough* isn't it obvious? *cough cough* remember 4 years ago? *cough cough* we swore to protect each other *cough cough* so even if i die *cough cough* i couldnt let bob kill you *cough cough* goodbye brother.'
back at evergreen terrace marge tries to console bart saying 'honey i know lisas death hurt but she would want you to move on' bart angrily yelled 'move on?! i cant until bob is dead! lisa died because of me! because i was too much of an idiot to save myself!'
later that day, at the school cafeteria, sophie krustofski notices bart shaking in fear like a lamb under the gaze of a hungry wolf while school bully Jimbo Jones cruelly subverted the lyrics of the bon jovi song you give love a bad name just to make bart feel worse by saying 'lisa was stabbed through the heart and you're to blame you give love a bad name."
outraged and disgusted by this injustice, sophie steps between them delicately pushing bart to the side and yelling 'how dare you?! bart is still in pain and you insist on digging the knife in?! whats your problem?!' She then pulls bart to her in a protective embrace like lisa would have and glares angrily at jimbo until he backs off. Sophie then turns to Bart and says 'forget about him. Lets grab lunch, don't worry, I'm buying.' After they sit at the table, Sophie says 'listen, I am super duper extremely sorry about your sister, lisa was the only other girl i felt comfortable talking to, you know?' 'anyway i promise you, bart i will help you avenge her." bart asks 'why did you help me?' sophie answers 'well I...' (she starts getting embarrased mid sentence). Bart asks 'you what?' sophie explains 'I this *kisses him on the lips*.' bart realizes 'you love me?' Sophie admits 'I do.'
That night they decide to walk over to herman's for a weapon to stab bob like he had to lisa. On the way sophie hears bart say 'its my fault lisa died. She died protecting me, I knew bob wanted to kill me but I still let my guard down, which is why he got me in that position in the first place. I'm pathetic, 4 years ago, Lisa and I... we promised to protect each other. I failed her, I am the world's worst older brother.' he buries his face in sophie's shoulder and breaks into guilty sobs.
Sophie objectively insists 'stop it! it is not your fault. You are acting like simba when scar blamed him for mufasas death. you're also destroying her memory by blaming yourself. You helped her so many times. You helped her when she felt threatened by allison, you helped her get revenge when those slumber party girls bullied her, you bought her that record when bleeding gums murphy died, and you helped her when she forgot to read wind in the willows for her test when she had a cold you are her hero bart. And i promise we will make bob pay for her death.' They get to the antique store and sophie gives him her hairpin to pick the lock. 5 minutes later bart comes out with a sickle.
When they get to bobs cell, bart is about to run in and kill bob but, sophie tugs his arm saying 'no! let me do it! you are all maggie has left she needs you! I need you!" Bart immediately has visions of sophie in extreme sorrow without him and of maggie growing up to be like toy story's sid or lock shock and barrell in her childhood, an emo teen or even a psychopath adult like black dahlia. Not wanting that future, he hands sophie the sickle.
final scene: sophie storms the cell, kills bob on lisas behalf, plants the sickle in cecils cell then she and bart leave proud knowing lisa was avenged and the cops will blame cecil for bobs murder instead of them.
The end
epilogue 20 years later bart said 'i hope you're watching from heaven, lisa, im hapily married to sophie, i learned martial arts so i dont have a repeat of what happened to you and to preserve your memory we named our daughter after you.'