Having closed its fourth season with the unidentified body of a young woman floating in the Ewing family swimming pool, Dallas launches its fifth season by casting suspicion of murder on both of the series' chief antagonists: the cunning, consciousless Texas oil tycoon J.R. Ewing (Larry Hagman) and J.R.'s lifelong enemy, attorney Cliff Barnes (Ken Kercheval). For a while, it appears as though J.R. is the guilty party, since he had the most motive. The dead girl turns out to be Kristin Shepard (Mary Crosby), the same person who had shot J.R. full of holes at the end of season three. Once this matter is settled, there are plenty of other crises to dwell upon. On the verge of breaking up her marriage with J.R., Sue Ellen (Linda Gray) sues for custody of her son, John Ross, at the behest of her current lover, Dusty Farlow (Jared Martin). This results in a confrontation between J.R.'s mother, Miss Ellie (Barbara Bel Geddes), and Dusty's millionaire dad, Clayton Farlow (Howard Keel) -- though this adversarial relationship will eventually dissolve in a surprising matter. Meanwhile, J.R. schemes to get even with Sue Ellen by temporarily shacking up with Serena Wald (Stephanie Blackmore)and scheming to financially ruin the Farlows; but at the end of the day, he relents and embarks upon a campaign to win Sue Ellen back (not for her sake, but so that he can wrest away custody of his son).
Elsewhere, the marriage between J.R.'s niece Lucy (Charlene Tilton) and medical student Mitch (Leigh McCloskey) comes to an end. Unable to have children of their own, J.R.'s brother Bobby (Patrick Duffy) and his wife, Pam (Victoria Principal), adopt a child named Christopher -- without revealing the fact that the child's biological parents are the late Kristin Shepard and her blackmailing paramour Jeff Farraday (Art Hindle). Cliff Barnes goes to work for his entrepreneur mother, Rebecca Barnes Wentworth (Priscilla Pointer), hoping to beat J.R. at his own game in the marketplace -- and in the process becoming almost as greedy and duplicitous as his rival! Conspicuous by his absence this season is Miss Ellie's husband, Jock Ewing. Although actor Jim Davis had died the previous season, the producers decided not to completely write out Davis' character of Jock Ewing, instead contriving a scenario whereby Jock is in South America on a mission for the government. Ultimately, Jock perishes in a helicopter crash, whereupon a grieving Miss Ellie finds solace in the arms of her former enemy, Clayton Farlow. In the series' traditional cliffhanger ending, Cliff Barnes, financially ruined and in disgrace thanks to the machinations of J.R., tries to commit suicide -- and if he dies, it will mean disaster for several of the main Dallas characters.