In September 1778 British troops were plundering fields and laying waste to cattle. This kept their army fed, and helped to deny food to the American troops. On the night of September 22, 1778, the Third Regiment of the Light Dragoons were stationed on Overkill Rd after several days of driving cattle out of the range of the enemy. They were trying to gain intelligence on enemy troop strength and position. The British, tipped off by local sympathizers slipped behind the patrols and went from farm house to farm house where the Dragoons were stationed and killed the entire patrol. There is speculation that Mr Blauvelt (one of the home owners where the troops were staying) was the one who betrayed the troops, since his house was not plundered by British troops afterwards.
The incident would remain largely forgotten, the bodies buried in small graves on the same farm where they died. 100 years later when relatives told the tale and showed local reporters the site, the story came to light, but it would be another 100 years before the graves were dug up, the bodies moved, and a proper marker placed in their memory.
For full details read this narrative which tells the story in much greater detail then you will read here.