Early in Act 1 of the Berkshire Theatre Group’s “The Lion in Winter, ’’ King Henry II, portrayed by Treat Williams, says jovially to his young mistress with a sweep of his arm: “Come, let’s go downstairs and meet the family.’’

Family? Scorpions in a bottle are more cuddly than the Plantagenet clan. But what malicious/delicious fun it is watching them scheme and connive and betray one another in this sterling production of James Goldman’s play, directed by Robert Moss.

“The Lion in Winter’’ unfolds during a not-so-festive Christmas in 1183 at Henry’s palace, where the main event is the no-holds-barred battle of wits between the British king and the wife he’s kept imprisoned for a decade but has now trotted out for the holiday, Queen Eleanor of Aquitaine, played by Jayne Atkinson.

Henry and Eleanor are at odds over which of their three sons will get to succeed him when he dies, but Williams and Atkinson suggest in their finely drawn performances that what actually lies beneath the royal duo’s verbal jousting and political jockeying is an undying love of the game, and, very possibly, each other.