The day of the wedding Turk picks up an extra shift at the hospital to get some extra time off for his honeymoon. Inevitably, what should be a very simple procedure turns into a life and death situation when Turk discovers complications with his patient and he gets stuck at the hospital. Meanwhile, a very stressed out Carla tries to manage the situation at the church while her groom is missing, her brother Mark continues to antagonize her, and her guests are becoming unnerving. After telling Elliot he is not in love with her, JD tries to put together the broken pieces of their friendship by getting Sean back together with Elliot.

The eve of Carla and Turk’s wedding gets off to a rocky start when Turk forgets to pick up Carla’s brother Mark from the airport. The mounting pressure does nothing to help Turk as he finds himself at a loss for words while writing his own wedding vows. Another relationship seems to be in trouble as well when J.D realizes that he does not love Elliot and goes to Danni for advice on how to tell her. Meanwhile, Dr. Cox is going through fighting withdrawals when Jordan refuses to fight with him anymore and the hospital staff pays the price.

J.D. and Danni breakup again because of J.D.’s continuing feelings for Elliot. When Elliot asks Sean to move in with her, J.D. decides he has to take action. Elsewhere, Dr. Kelso and Dr. Cox face-off over whether or not the hospital should provide full body scans. As the wedding grows nearer, the pressure to make their special day perfect starts to get the best of Carla and Turk.

After an unexpected night of passion with Elliot, J.D is left frozen in shock when Sean comes back into Elliot’s life. Carla and Turk try to pass on advice to J.D but despite their efforts he finds himself in bed with a reinvented Danni on the rebound. Dr. Cox is shocked by the realization that his hatred of Dr. Miller may actually be an attempt to mask a secret crush. Meanwhile, Dr. Kelso and the Janitor square off on the do’s and don’ts of hospital security.

J.D is left bored after he clears his schedule to help Dr. Cox with a special project only to be pushed aside for a new intern. With some free time on his hands JD offer to help Elliot with Kids Day when she discovered she couldn’t attend. His good deed does not go unnoticed, even though Sean shows up unexpectedly. Meanwhile, Turk begins to get nervous about the wedding when he has to send out the invitations. Dr. Cox and Dr. Kelso end up fighting for the attention of the new female doctor, Dr. Miller.

The return of Dr. Ron Ramirez to Sacred Heart from his philanthropic work abroad, sparks some doubts in Carla’s mind about her feelings for Turk. When she accepts a dinner date with him, J.D. is torn between telling Turk the truth and keeping his promise to Carla. Back at the hospital, Elliot takes a stand for her patient despite the fact that Dr. Cox believes he is a drug addict faking abdominal pain to get medication. Meanwhile, the Janitor introduces J.D. and Turk to his “twin” brother, but they aren’t buying it.

In a unique episode, the path of a butterfly is the deciding factor in the fate of the young doctors. At the beginning, a butterfly landing on a woman’s breast sets off a chain of events ultimately resulting in the death of J.D. and Turk’s patient, leaving them to wonder what they could have done to change the outcome of their day. Taking a step back in time, the butterfly takes a slightly different path, landing instead on a man’s chest setting in motion an alternate chain of events that leads our characters down a very different path. Will this be enough to change the fate of their patients?

Jordan’s friends Allison and Maddie come to town to provide moral support for Jordan after her brother’s death — however, their constant presence does not provide any relief to Dr. Cox. Meanwhile, Turk tries to impress the new female surgeon, Dr. Miller, but his first encounter serves only to leave him baffled by the opposite sex yet again. Attempting to reinforce the policy on sexual harassment at Sacred Heart, Carla is forced to teach a course where Dr. Kelso is the number-one student.

Danni and Jordan’s brother, Ben returns from traveling the world, a trip he’s been on since his leukemia went into remission. When Dr. Cox learns he hasn’t seen a doctor since he left, he recruits J.D to do a thorough work up. Unfortunately, forcing J.D. to drop his other patients to run tests on Ben is a decision Dr. Cox soon regrets. Meanwhile, Elliot’s concern about a bunion on her foot leads to the revelation that Carla has been hiding something from Turk.

Elliot finds herself perplexed over a simple procedure that leaves her questioning her career path. She goes to seek Dr. Kevin Casey’s advice but becomes frustrated when she learns that the epiphany toilet, which the Janitor secretly installed on the roof, is getting more attention than she is. Meanwhile, Turk asks JD to be his best man at his wedding, which sends JD into sheer bliss momentarily until he hears a phone message that makes him question his friendship with Turk.