"Mars, Bars" is the fourteenth episode of the third season of the American mystery television series Veronica Mars, and the fifty-eighth episode overall. Directed by Harry Winer, with a story by Phil Klemmer, John Enbom, and Joe Voci and a teleplay by Klemmer and Enbom, the episode premiered on The CW on February 20, 2007. The series depicts the adventures of Veronica Mars (Kristen Bell) as she deals with life as a college student while moonlighting as a private detective.

The episode is the second of two to deal directly with the death of Hearst's basketball coach, Tom Barry (Matt McKenzie). In this installment, Veronica and Keith (Enrico Colantoni) search for Tom's missing son Josh (Jonathan Chase) while investigating a variety of alternate suspects. In addition, they continue to question Mindy O'Dell (Jaime Ray Newman) and Hank Landry (Patrick Fabian) with regard to the death of Dean Cyrus O'Dell. Meanwhile, Logan (Jason Dohring), Parker (Julie Gonzalo), Mac (Tina Majorino), and Bronson (Michael Mitchell) attend a scavenger hunt for Valentine's Day.

"Mars, Bars" marks the final appearance of series Michael Muhney, the actor of Sheriff Lamb, after the death of his character. Muhney was not informed of his character's death until the filming of the episode; he was surprised and saddened at the decision. Spoilers about the scene were not leaked prior to the episode, something about which Muhney was happy. In addition, Mac was initially scheduled to be taken advantage of by a professor in this episode, but a romantic relationship with Bronson was chosen instead. The episode garnered 2.27 million viewers and positive reviews from television critics, with many praising Muhney's performance and viewing it as a return to form for the show, while some were more critical of Logan's subplot.

At the end of the previous episode, Postgame Mortem, Veronica is arrested by Sheriff Lamb (Michael Muhney) on the suspicion that she helped the now-missing Josh Barry to escape from prison. This episode opens with Lamb questioning her and learning little, as she had nothing to do with his disappearance.

Keith, Veronica's father and owner of Mars Investigations, their detective firm, visits Veronica in jail. Cliff McCormack (Daran Norris), a local public defender, also arrives, and tells Veronica that she has been all but cleared, but Sheriff Lamb will keep her in custody for as long as he can because he still believes she was involved in Josh's disappearance. Keith returns to Mars Investigations, where Hank Landry arrives and says that he found a bugging device in his phone. Landry had been implicated in the ongoing investigation into the death of Cyrus O’Dell, dean of Hearst College where Veronica is a student. Keith denies that he or Veronica placed the device in his phone, but Hank becomes angry, telling him to stop investigating him.

Keith brings his findings on the death of Cyrus to Sheriff Lamb and provides an alternate explanation; that the Dean had discovered his wife was having an affair. Lamb agrees with him that it was a murder. Lamb calls Mindy O'Dell, the dean's wife and a main suspect, to his office. Logan, Veronica's on-again, off-again boyfriend, visits Veronica in her cell and they are civil to each other. After being released from jail, Veronica is stopped on the street by Josh, who has Mason (Robert Ri'chard) in the trunk of his car, frantically telling Veronica that Mason is the culprit. When Veronica disproves this claim, she tells Josh to call her using a disposable phone within 24 hours. Veronica releases Mason from the trunk.

Logan takes a wireless card to Mac as a favor, and she, Parker, and Bronson invite him on a night out. Logan, Mac, Bronson, and Parker take part in a Valentine's Day scavenger hunt. The quartet find their last clue at a beach. Mac and Bronson kiss, while Parker and Logan bond while swimming. The scavenger hunt ends, and they come in third place. Logan and Parker leave, and Mac and Bronson have sex for the first time.

While reviewing the O'Dell case, Veronica notices that the TV station the dean was watching the night he was murdered had moved its programming back an hour, meaning their estimated time of death was wrong. The forensic results about the prints in O'Dell’s room come back, and they are the fingerprints of Steve Botando (Richard Grieco). Steve Botando is investigated by Sheriff Lamb.