The summer of 1758 was spent by Forbes in mobilizing 6,000 motley troops from colonial militia and regular army and building a road over the Raystown Path.  On September 14, 1758, an advance party of 800 Highlanders and provincials under blustering, hot-headed Maj. James Grant (Baldwin's description; Grant was also Scots, natch) appeared on the hill that overlooked Ft. Pitt, later named Grant's Hill. Grant determined to usurp Forbes and developed a plan to draw the French and Indians from the fort and into an ambush. Virginia frontiersman Maj. Andrew Lewis was sent forward with 400 men, each with a white shirt "to prevent mistakes" and ordered to bayonet the sentries and attack the Indians around their campfires. However, Lewis returned later complaining that his men were hopelessly lost in the fog and pre-dawn darkness and were wandering around among the fences, cornfields, and fallen logs outside the fort.  Grant was furious and sent out another 50 men to attack a cabin that scouts had reported as surrounded by Indians. Finding the cabin empty, they  set fire to the cabin, exposing themselves to the French forces in the fort. Grant compounded the problem by recalling the original 400 man force and sending them to the rear and then further spreading his troops by sending out another 100 to reconnoiter the fort after the fog had lifted.  When he received word that some Indians had discovered his left flank, near the Monongahela River, Grant felt he had lost any chance at surprise and had his drums beat reveille "to put on a good countenance and to convince our men they had no reason to be afraid." This, of course, brought the French and Indian forces swarming out of the fort and adjacent buildings in a rather foul mood.  They attacked the Highlanders at Grant's center and simultaneously snuck parties up each river bank and attacked his flanks. Confusion quickly reigned and the men began to scatter. Lewis' force tired to come forward to support Grant, but he somehow missed the main force and succeeded only in adding to the confusion.

Grant wrote later that he hoped he would "never see again such a pannick [sic] among the troops." About 270 men were killed or captured as the British frantically retreated through the tangled woods around the fort, trying to sprint the entire 50 miles to the safety of the main camp at Loyalhanna. Grant managed a small rear guard which fought its way to where a Capt. Bullett had been left, with 50 Virginians, with the company's baggage. Here they held out for a short while. When all seemed lost, Bullett hoisted a white flag and he and his men emerged with their rifles held above their heads. They walked forward to the advancing French troops until, when they were only a few yards away, the Virginians swung down their rifles and began firing. The Virginians then charged the French with their bayonets. As the opposing troops scattered, Bullett and his men escaped.  During this action, Bullett stumbled across Grant along the bank of the Allegheny River with his head in his hands, moaning, "My heart is broke; I shall never outlive this day." Bullett urged to forget military honor and head for the hills, but Grant refused to leave the field of battle as long as there remained one man willing to fight. Bullett followed his own advice, leaving Grant and his men to make a final stand along the river. At first, the French and Indians held their fire, trying to take Grant and his men prisoner, but when they refused to surrender, the larger force opened fire, driving the British troops into the river. A few may have managed to swim off, but Grant was surrounded and captured.   The fallout from this event was that Grant tried to pin the folly on Lewis. Grant managed to sneak out a letter to that effect, but it was intercepted by Indians and handed over by the fun-loving French to Lewis, who was also a prisoner at Ft. Pitt. Lewis immediately found Grant and challenged him to a duel, which Grant refused. Lewis then settled the manner through the time-honored tradition of spitting in Grant's face. Apparently this ended the matter, although Lewis later extracted revenge on the entire British regular army as a general in the Revolutionary War.

Five of the prisoners were burned at the stake. Several more of the "petticoat warriors" (as Highlanders were called by the Indians) were decapitated and their heads placed on peeled stakes around the Indian racetrack at the fort.  Their kilts were placed derisively around the stakes. Supposedly one Highlander claimed he could mix a concoction that could make any part of the anatomy invulnerable, which the Indians took him up on. He smeared the concoction on his neck and signaled for the ax to drop.  The poor gent was either very, very wrong or was literally having the last laugh. Either way, his head rolled. 

On Nov. 25 of the same year, Forbes' main force reached Ft. Pitt. As they marched on the fort, the provincials (colonial militia) went first, passing the staked skulls of the dead Highlanders on their march. After they passed, though, the Highlanders under Forbes' command, marching behind the colonists, came upon the same gruesome sight. The colonists heard a buzzing emanate from behind, which soon turned to an angry roar. The enraged Highlanders, their muskets cast aside and only their deadly, naked claymores in their hands, rushed past the provincials swearing vengeance on the French and Indians. But when they reached the fort, the enemy was gone and only the smoldering remains of the abandoned fort were left.