In the opening scene, Kevin asks Eve out for dinner at Mario's.

Scotty is finally released from jail. He wants to celebrate so he asks Lucy out on a date. They too, decide to go to Mario's.

Chris is working in the lab. He is recording the effects of the DL-56 mixed with the Eve's strain of flu. Apparently the DL-56 accelerates the virus when mixed. Chris is interrupted by Frank. Frank is concerned about possible side effects that the drug might have on unborn fetuses. Chris asks Frank if Julie is pregnant. Frank believes that she is, however she does not know for sure. He wants to find Kevin to have him persuade Julie to take a pregnancy test.

Courtney told the Connellos that Joe is really Neal's father. She thinks it is time for the truth to come out.

The Connellos visit Neal at the Scanlon's house. They blame Courtney for their son's death. While Neal is outside playing basketball, Mr. Connellos asks Mary if she knows anything about Joe being the father of Neal. Mary told him that she knows nothing about this and volunteers to go inside to call Joe and find out the truth.

At the hospital, Karen argues with Courtney. She calls her a self serving manipulator. She does not agree with Courtney's methods.

When Courtney and Joe arrive home, they find Mary but no Neal and no Connellos.

At Mario's, Lucy orders the best bottle of wine for their celebration. In walks Eve and Kevin. Neither party seems happy to see one another. Lucy is still jealous of seeing Kevin with any other woman, especially Eve. Kevin wants to just completely ignore the other couple and continue on with their date. Lucy is unable to ignore the other couple. She makes a couple of unnessecary comments regarding Eve's dress. This conversation leads into another conversation between Scotty and Lucy. Lucy believes that the only reason that Scotty is with her is because she represents safety.

Chris is at the lab. He decides that he is going to destroy this new strain of DL-56 that he has created. He finds it missing. He remembers back to Frank saying that he will take as much of the syrum that he wants to. Chris rushes out of the lab intending on stopping Frank from taking any of this syrum.

At Mario's, Lucy and Scotty are talking about committement. Lucy is trying to explain why it is not a good idea for her to remain at the Firehouse with Scott and Serena.

Kevin and Eve talk about moving on. Kevin told Eve that she is the most beautiful, entertaining woman that he has ever met.

Frank arrives at Mario's. He is not feeling well since he took a shot of the wrong DL-56. He thinks he is coming down with the flu. Chris arrives and asks to exchange the vials of DL-56. Chris is worried when he finds out that Frank has taken some of syrum. Frank went to hand him the vial and it slips out of his hand and breaks on the floor. Does this mean that everyone at Mario's will be infected with this deadly strain of the flu?

When Courtney, Joe and Mary realize the Kanelloses chartered a private plane to take Neil to Greece, Joe and Courtney make plans to go to Athens. While Courtney is upstairs packing, Mary asks Joe if Neil is really his son. Joe apologizes for not telling her sooner, explaining the situation they were in. Mary starts cursing the Kanelloses for taking Neil and told Joe that Neil is lucky to have him as a father. Mary then confronts Courtney about her silence all these years. Courtney promises to make it up to all of them when they bring Neil home. Joe heads over to GH to fill Karen in on their plans. She told him that she wants to go with them. He asks her to stay and watch out for Frank and Mary. Karen reluctantly agrees.

Meanwhile, on the plane, Neil laments to his grandparents how sad it is that his mom wasn't able to make the plane in time. They smile and tell him that they'll send another one back for Courtney.

At Mario's, Scott tries to convince Lucy to stay at the firehouse, regardless of the nature of their relationship. Lucy has her doubts as to whether or not it would work. She gets jealous when she sees Kevin and Eve sharing their dessert. At Kevin's table, Lark apologizes to Eve for thinking she was the killer. Eve accepts her apology.

Chris frantically wipes up the spilled DL56 compound on the floor of Mario's. Frank realizes he's really sick and Chris takes him to the bathroom, where winds up laying on the floor. Chris told him that he stole the wrong batch of the drug, but his reaction might just be from having the flu.

Lark asks Kevin to check on Frank. Kevin finds him slumped on the floor in the bathroom, where Chris is burning the towels he used to clean up the DL56. When Kevin asks about the fire in the trash can, Chris covers by saying someone left a lighted cigarette. Kevin and Chris heave Frank up and start to take him out of the bathroom. Eve sees them and demands that someone call an ambulance. Chris brushes her off, saying that Frank probably has the flu. Suddenly, Frank passes out and falls to the floor. When Chris still refuses to call an ambulance, Eve pulls him to the side and asks him what's going on. He tries to make light of the situation, but she isn't buying it. He told her that he mixed her virus with a compound he was developing to combat the flu, only the results were disastrous and now Frank has come in contact with it. Eve asks if anyone else has been contaminated. I don't think so, Chris says.

At the firehouse, Lucy and Scott return from dinner. Lucy realizes she doesn't feel well--and it just hit her on the way home.

At the firehouse, Lucy develops chills and fever, and Scott tries to pamper her with hot tea, magazines, and catalogs. Karen calls to welcome Scott home from jail and learns that Lucy is feeling ill. She told Scott that Joe has left for Greece with Courtney.

At Mario's, Frank's condition worsens, and Eve calls an ambulance. Chris reminds her to tell the paramedics to wear masks. While they wait for the paramedics to arrive, Eve confronts Chris about his research, but he continues to evade the truth about his having mixed the Nepalese Flu virus with DL-56. When Kevin notices that Lark is beginning to cough, she told him it is only a nervous reaction. When the paramedics arrive and ask Frank if he is taking any medications, he told them no. On the airplane, Joe and Courtney encounter an old woman who mistakes them for honeymooners. While Courtney is out of her seat, Joe calls Karen and told her to check her mailbox, where he has left her some hearts with suggestive little poems on them. Courtney overhears the end of Joe's conversation with Karen and takes the opportunity to remind him of how she used to slip poems under his pillow when they were in college. A while later, Courtney becomes emotional remembering the Christmases when Neil was sick. Joe comforts her and suggests they get some sleep so they will be ready to search for Neil once they land. Courtney complains that she can't sleep and squirms around restlessly until she ends up with her head on Joe's shoulder.

The paramedics bring Frank into the ER, and Ellen begins to examine him. She orders several tests, worried that she hasn't seen so severe a case of the Nepalese flu.

Lucy drifts off for a while and awakens feeling much worse. When she tries to stand up to go to bed, she collapses in Scott's arms. He puts her back on the couch and offers to call Karen to ask if she'll stop by to check on Lucy's condition. Lucy rejects the idea because she doesn't want anyone to get sick from coming into contact with her. While Frank is being treated, the ER gets a call that Lark has begun to show symptoms and is on her way in. Kevin suggests they contact everyone who was at Mario's, but Ellen doesn't want to cause a panic. Instead, Kevin calls the firehouse and told Scott about Frank's collapse and the seriousness of the illness.

Eve corners Chris again and presses him for information about his research, he finally admits that he is afraid the virus may have mutated.

Eve continues to press Chris for more information about the compound he mixed with the virus culture, but he refuses to tell her anything, even after Ellen shows them results of Frank's blood tests, which reveal the mutated virus is a particularly virulent strain.

When Scott carries Lucy into the ER, Ellen begins her treatment after asking if they had dinner at Mario's that evening.

As Frank's condition worsens, Eve convinces Chris that recreating his "herbal" mixture may help them find a treatment for the mutated virus. He agrees to try, and Kevin volunteers to help them in the lab. Just then, Kevin hears Ellen calling for help with Lucy. Eve told him to go to Lucy, and Kevin promises to meet them in the lab as soon as he can. When paramedics bring Lark into the ER, Mario asks Chris if he has any idea why the outbreak seems ties to his restaurant. Chris evades the question and told Mario to keep an eye on Lark.

While Ellen is treating Lucy, Scott begins to develop a cough. Ellen takes Scott to another exam room to give him a shot, and Kevin arrives to help take care of Lucy. When Lucy's breathing becomes labored and she develops chills, Kevin holds on to her until she feels better. Lucy drifts off to sleep, and Scott returns to the exam room. Kevin leaves for the lab, and Scott takes up vigil at Lucy's bedside.

Lark insists on seeing Frank, who regains consciousness long enough to tell her that he believes he has gotten sick from the new DL-56 formula that Chris has developed. He begs her to find Chris and get him some of the original formula.

In the lab, Chris continues to conceal the true nature of his research from Eve, listening to his recorded notes using an earphone. When Eve mentions that he is beginning to develop flu symptoms, Chris notes that Eve is not getting sick. She hypothesizes that her exposure to the original virus may have made her immune.

Between waking and sleeping, Lucy calls out for Kevin, but awakens to find Scott at her side. Burning with fever, she asks Scott to cool her down by telling her stories about Canada. When her fever once again turns to violent chills, Scott climbs onto the gurney with her and holds her in his arms to keep her warm.

Kevin catches Lark trying to leave the ER, she explains that she has to find Chris immediately. Kevin offers to find him for her and has her taken back to bed. Kevin notices that Ellen is also developing symptoms, though he is not. Kevin heads off for the lab while Ellen talks to Matt on the phone. Matt offers to help out in the ER, but Ellen persuades him to stay put. She told him she plans to close the ER in hopes of containing the outbreak. He agrees to stay away, but offers his help if she needs it. After hanging up, Ellen calls the Association for Disease Control to ask for help.

Moments after Kevin arrives at the lab, Chris collapses, and the tape recorder on which he has made his notes went flying into a beaker of acid.

Ellen calls the Scanlon house to inform Mary of Frank's condition. Mary wants to go to the hospital, but Ellen told her the ER is under quarantine. Karen takes the phone, and Ellen told her that Scott is also sick with the flu. Karen leaves for the hospital, promising to call Mary as soon as she has any news.

Association for Disease Control doctors have arrived at GH, and one of them prevents Matt from entering the ER. When Karen arrives, she and Matt conspire to get into the ER. Karen fakes symptoms while Matt told one of the ADC guards that he has to get her into the ER for treatment. Once inside, they find isolation suits to wear to protect them from the virus.

In the lab, Chris's condition worsens while Eve told Kevin that all of Chris's research was on the tape destroyed by acid. While Kevin tries to rouse Chris to get some information from him, Ellen calls to inform Eve that she plans to ask the ADC virologist to come to the lab to help determine what has caused the virus to mutate.

Still sitting at Lucy's side, though he is quite sick himself, Scott calls Gail to check on Serena and ask her to postpone Serena's birthday party. Gail agrees and puts Serena on the phone. Scott explains that he wants Serena to stay with Gail and Lee because both he and Lucy are sick. Serena agrees, saying she wouldn't want to have her birthdaY party if Scott and Lucy can't be there. Lucy takes the phone from Scott and promises to throw Serena a big party just as soon as she is feeling better.

In the ER, Karen and Matt check in with Ellen, who is growing sicker by the minute. She sends Karen off to check on Lucy and Scott and catches Matt up on Eve's theory that Chris's research caused the virus to mutate. She asks Matt to go up to the lab to help Eve and Kevin take care of Chris.

The ADC virologist questions Frank in an attempt to discover how he contracted the virus. Once again Frank lies when he is asked if he is taking any medications. Ellen comes into Frank's room and told the virologist about Eve's suspicions the virus mutated during Chris's research. He volunteers to go to the lab and help isolate the mutating agent.

Karen arrives in Lucy's room and tries to persuade Scott to go to his own bed. He refuses to leave Lucy's side. Karen checks Lucy's breathing and determines that she needs to be put on a ventilator to keep her lungs clear of fluid. Ellen stops to check on Lucy after Karen has put her on the ventilator and Karen leaves to check on Frank. Seconds after Karen leaves, Ellen collapses into a chair.

When the virologist arrives at the lab, he and Kevin begin looking through the lab computer files to see if Chris has left any trace of his research. Eve brought Matt up to speed on their attempts to recreate Chris's research. Unsurprised that Chris was responsible for the mutated virus, Matt begins to work on him, hoping to keep him alive long enough for them to learn how to stop the disease.

While Karen is checking on Frank, he drifts in and out of consciousness. Lark comes into the room and told Karen that Frank's illness was caused by the new DL-56 formula developed by Chris.

The ADC supervisor arrives at the lab and announces that they have to shut it down in order to prevent further risk of contamination.