Politically, Rob was sympathetic to the Jacobite cause – the attempt by the exiled House of Stuart to re-establish a Catholic monarchy. It is said Rob had a preference for raiding the land-holdings of those who took the opposite political view. However, his reputation as a cattle dealer soon increased to the extent that the Duke of Montrose arranged for Rob to select cattle on his behalf (for fattening and resale). As much as £1000 changed hands but the deal went badly wrong. Mysteriously, Rob’s head drover disappeared with the money. In equally murky circumstances, the Duke had Rob declared an outlaw before giving him a chance to repay the money. He seized Rob’s lands at Craigrostan on the east side of Loch Lomond, and burned down Rob’s house.
Historians have for long debated the motive of the Duke of Montrose. Simple greed for more land? A political move because he was against the Jacobites and suspected Rob of Jacobite plotting? Whatever the reason for Montrose’s actions, from 1713 to 1720 Rob lived beyond the law. It is from this period that many of the tales of Rob as a kind of Highland Robin Hood originate.
Rob swore revenge on the Grahams, the family and kinsfolk of the Duke. He organised bands of sympathisers, raided Montrose’s cattle and collected rent from Montrose’s tenants, usually just ahead of Montrose’s factor (manager), Grahame of Killearn, who often seems to have been a victim of Rob’s activities. (Factor’s Island by Stronachlachar on Loch Katrine recalls one incident when he was held hostage there by Rob.)
Rob took part in the 1715 Jacobite rebellion and had many narrow escapes. He was actually captured three times but by guile and skill escaped every time. He also took part in the 1719 rebellion but by 1725 seems to have made peace with the authorities, eventually receiving a pardon from General Wade, the famous Highland road-builder.