The army got John Adcock out of prison. It wasn't a dramatic rescue, but a bit of administrative good fortune. Adcock had been convicted of "riot", a crime more or less equivalent to disturbing the peace, and was sentenced to six months in prison in Warwick, England. The fact that Adcock was a private soldier in the 38th Regiment of Foot did not exempt him from being convicted and having to serve his time.
As long as the regiment was on service in Great Britain, that is. In early 1774, while Adcock was in prison in Warwick, the regiment was ordered to America, part of a military force that was expected to quell the rebellious spirit that had taken over Massachusetts. The 38th was currently in Ireland; how Adcock came to be in prison in Warwick is not known - he may have been on recruiting service, or on furlough. When word came that his regiment was to embark for America, his sentence was remitted, and on 31 March 1774 he left Warwick to join his regiment.
The 38th arrived in Boston that summer and encamped with several other regiments on Boston Common, a strong military presence intended to restore order through intimidation. There seem to have been no repercussions for Adcock's having been in a civilian prison. He was, in fact, a good enough soldier that he was appointed corporal on 17 September, but his time in that capacity was short; on 15 October he was reduced again to the ranks. Such short-term appointments were not unusual, and did not always denote poor discipline. Sometimes men were appointed to temporarily replace corporals who were indisposed, and sometimes men who were appointed didn't care for the roll and requested to be reduced.
Whatever the reason for his reduction, it didn't prevent him from being put into the regiment's grenadier company on 15 April 1775, a move probably made to bring the company up to strength for the impending expedition to seize rebel stores in Concord. There's no indication that he was wounded in that action, or in the assault on Bunker Hill in June. The next detailed information we have about John Adcock is from June 1779.
The 38th Regiment's grenadier company, as part of the 1st Battalion of Grenadiers, had spent the winter quartered on Long Island, part of the British garrison centered in New York City. With the opening of the campaign season, the battalion was part of a force sent up the Hudson River to secure British points at Stony Point and Verplanck Point. The grenadier battalion was among the troops that established an encampment on the east side of the river, fortifying Verplanck Point while awaiting their next move.
Something was amiss with discipline in the battalion, however, which led to a spate of desertions. It may have been simply the relative freedom of being out of quarters, or the opportunities for marauding afforded by close proximity to the front lines, or issues internal to the battalion itself. Several grenadiers were caught and brought to trial, but about two dozen got away, including John Adcock.
The 38th Regiment served out the war in America and was among the last to leave New York in November 1784. They returned to Great Britain, and there soldiers who were no longer fit for service were discharged. But amid all of the discharges, a man was added to the rolls: John Adcock, "joined from desertion" on 23 April 1784. We've found nothing about his whereabouts for the intervening years, including how he managed to get back to Great Britain. Quite possibly he had joined an American privateer crew, been captured at sea and sent to a British prison. He may have enlisted in a Loyalist regiment that was disbanded at the end of the war and received passage to Great Britain from the army. There are many possibilities. No matter; his soldiering days were over. Just a month after rejoining his regiment, John Adcock was discharged, and there's no evidence that he returned to the service.