This account of the action on June 20, 1776 is taken from "Sea of Glory---The Continental Navy Fights for Independence 1775-1783" by Nathan Miller (1974):
A month after the British had evacuated Boston---and well before the news had reached London---a convoy of thirty-five tarnsports carrying three thousand Highland troops sailed from Scotland for America. A few days out, the fleet was scattered by a storm. Most of the transports arrived in the Boston area while the British squadron was still there and joined with it. But several of the vessels arrived after after the British navy had left. They plopped into the Yankee net like codfish. First prey for Washington's fleet was the troopship Anne, taken by the armed schooners Lee, Lynch, and Warren along with 110 men from the 71st Highland Regiment. Fired by the capture and reports that more transports were blindly on the way, the crews of the schooners eagerly scoured the sea lanes where they were expected. Several attacks were launched against the wallowing troopshops but in each case Royal Navy frigates came up in time to stop the fight.
On June 15, the transports George and Arabella sighted Cape Ann after a rough passage. Having no inkling that Howe had abandoned Boston, they were not surprised to see four schooners coming out to meet them...to the shock of the Scotsmen, the schooners opened fire without warning...the transport's 6-pounders were ordered to reply and the schooners broke off the fight. Pushing forward into the harbor they expected protection from a fort or a British ship...but a Yankee 18-pounder mounted on a headland opened up on the Arbella, which ran aground in the direct line of fire. A mixed barrage of round and grape shot slammed into the transport and her flag was quickly hauled down. Then the Yankee gunners turned their attention to the George. There was no return fire, so in the descending darkness it was presumed that she, too, had struck. That was the last thing that the Highlanders' commander had in mind. Too far into the harbor to retreat, especially now that the wind had died away, he ordred the vessel anchored and prepared for action.