In the 1500's, the border lands between England and Scotland were very lawless and wild. Families lived by stealing each other's cattle, capturing and ransoming members of opposing families, and variants of the above, usually involving cross-border hatreds, but often ganging up with a family on the opposite side to attack someone on one's own side of the border. Alliances came and went like the weather. The law was represented fitfully by six "policemen" or "sherriffs", three on each side, known as Wardens of the March.
Into this bed of coals walks James Hepburn, Earl of Bothwell, Mary Queen of Scots' lover, who doesn't half fancy himself to sort these low-lifes out. He is appointed Warden of the Scottish West March (where we Elliots come from originally). On his first day in the job, complete with his effete band of fancy friends from Edinburgh, he drops off the baggage at Hermitage Castle (which comes with the job), and goes in search of a miscreant to punish. He encounters one John Elliot, aka "Jock o' the Side". He shoots. Jock falls off his horse. The Earl walks over to make the arrest. Jock jumps up, unhurt, he was faking, and holds a knife to the Earl's throat. Controlling the whole crowd via his hostage, Jock forces them all back to Hermitage, where it transpires that another band of Elliots have overwhelmed the servants, taken the castle, and are looting the fancy baggage.
James Hepburn, Earl of Bothwell, Mary Queen of Scots' lover, ends his first day in the job negotiating with a band of raggedy-ass Elliots to get his life and castle back.
Which the family motto is "Nemo me impune lacessit": Nobody Screws With Me and Gets Away with It.
We didn't, really; as shown in this diagram below, which shows the Border Families, and who was feuding with whom (Source: The Steel Bonnets, by George Macdonald Fraser - author of the Flashman stories, and lots of other good stuff.)