"Jughead" is the third television episode of the fifth season of ABC's Lost. The eighty-sixth episode of the show overall, "Jughead" aired on January 28, 2009 on ABC in the United States, being simulcast on A in Canada. The episode was written by supervising producers Elizabeth Sarnoff and Paul Zbyszewski and directed by Rod Holcomb.
The episode opens with a flashback of Desmond Hume (Henry Ian Cusick), in the Philippines, searching for a doctor to help his wife Penny Widmore (Sonya Walger), who is giving birth to their son, Charlie. In 2007, Desmond and Penny arrive in London, where Desmond plans to look for the mother of Daniel Faraday (Jeremy Davies), who is believed to be at Oxford University. However, the school has no record of either Faraday, even though Daniel was a professor there. Desmond searches Faraday's lab and meets a janitor who tells him that Faraday conducted experiments on a woman and provides an address for her. At her house, Desmond finds that the woman is in a vegetative state after experiencing temporal disassociation, similar to Desmond's experiences on the freighter (as seen in "The Constant"). He learns that Penny's father, Charles Widmore (Alan Dale), is not only paying her medical expenses, but also funded Daniel's research. Desmond confronts Widmore, who gives him the address of Daniel's mother in Los Angeles. Desmond returns to Penny, who agrees that they must travel to Los Angeles.
In 1954, following the events of the previous episode, "The Lie", Juliet Burke (Elizabeth Mitchell), John Locke (Terry O'Quinn) and James "Sawyer" Ford (Josh Holloway) interrogate the two men they have captured. Juliet deduces that they are members of the Others because they can speak Latin. One of the men, a younger Charles Widmore (Tom Connolly), kills the other when he agrees to help Juliet, Sawyer, and Locke, and flees to his campsite to warn Richard Alpert (Nestor Carbonell). Locke follows him and meets with Alpert, using Jacob's name and the compass Alpert gave him to gain his trust; however, Alpert is not entirely convinced. Locke tells Alpert to visit him after he is born in 1956 (a visit depicted in the episode "Cabin Fever", during which Alpert shows a young Locke the compass), but cannot convince Alpert to show him how to leave the island before the next time jump occurs.
At the same time, the freighter team, consisting of Miles Straume (Ken Leung), Charlotte Lewis (Rebecca Mader) and Daniel Faraday are captured by another group of Others, led by Ellie (Alexandra Krosney). Faraday deduces that the American military has come to the island to test hydrogen bombs, and that the Others are in possession of one which is leaking radiation. He convinces Alpert to let him defuse the bomb, confessing his love for Charlotte as proof that he won't detonate it on purpose. Ellie leads Faraday to the bomb (the titular Jughead), and after an inspection he advises her that the bomb should be buried and will not go off for at least 50 years, inadvertently revealing that he is from the future. Ellie doesn't believe him, but Juliet and Sawyer show up and disarm her. The time jump occurs and the group is safe, but Charlotte suddenly collapses with a nosebleed.
"Jughead" is the first episode of Lost to be co-written by Paul Zbyszewski, who joined the writing staff prior to the start of production on season five. Elizabeth Mitchell learned as much Latin as she could for the episode. Mitchell said she could not "just learn it phonetically", so she spent the "whole weekend" trying to learn the language on the phone with a Latin professor.