Season 5 begins with Fiona balancing her job and a crush on her older boss. Meanwhile, Lip leaves college and heads back home to work a demolition job; Frank unveils the secret project he's been working on; Ian helps a pregnant Svetlana take care of baby Yevgeny; and Kevin plays stay-at-home dad when Veronica goes to work at the Alibi.
Frank tries to scare off the two lesbians who are buying up property in the neighborhood; Debbie throws a wild party; Fiona agrees to go to a concert with Davis; Carl discovers a hidden talent; Ian goes on a crazed cleaning spree and asks Lip to help convince Mandy not to move to Indiana with her abusive boyfriend.
Frank tries to retrace his steps after an epic bender to find what he did with his six-figure insurance settlement; Gus admits he is falling in love with Fiona; Lip visits Amanda in Miami; Carl starts a new job as a drug dealer; Debbie develops a new crush; Debbie begins training at Derek's boxing gym; Kev blows off a date because he doesn't want to leave the girls with a sitter.
Fiona and Gus navigate the awkwardness of their quickie wedding, but her plans to announce the marriage at a family dinner unravels when a coworker overdoses on heroin. Meanwhile, Frank avoids an irate Sammi; Debbie trains at Derek's gym; Mickey grows more concerned with Ian's erratic behavior; and Lip decides to head back to school early.
Newlywed Fiona struggles to remain faithful when Jimmy returns and relentlessly pursues her; Ian steals Mickey and Svetlana's baby; Sammi takes over the Gallagher house and enforces strict curfews; Debbie starts high school; Veronica grapples with her decision to separate from Kev.
Ian gets upset when he learns he is under a mandatory 72-hour hold at the psych ward; Frank returns home from the hospital and refuses to apologize to Sammi; Jimmy and Gus have a face-to-face meeting about their futures with Fiona; Lip discovers he never filled out his financial aid forms and now owes thousands in tuition; Debbie tries to get out of the "friend zone" with Derek.
Ian returns home from the psych ward but refuses to accept his bipolar diagnosis or take his medication; Gus tells Fiona he is going on tour and that they need time apart; Frank recovers from his gunshot wound and plots revenge against Sammi; Carl is asked by his boss to run drugs to Indiana; Lip convinces Kev to sell drugs in the dorms.
Frank plays tour guide to the seedier side of life for his doctor after she is diagnosed with terminal cancer; Fiona prepares Carl for his sentencing hearing; Lip sleeps with a professor; Ian realizes he needs to get back on his meds.
Frank starts to enjoy the company of his new sick friend and formerly uptight doctor, but she dumps him when she suspects he is developing feelings for her.
Frank becomes concerned about Bianca's increasingly erratic and dangerous behavior.
Season 5 ends with Fiona reuniting with Gus after he returns from his tour, but she struggles with the fact that her feelings for Sean have turned into love. In Costa Rica, Frank has love struggles of his own while he works to keep Bianca happy.