Meanwhile, Sherburn had sent a man ahead to learn what was happening at the fort. The man returned with news that Forster was marching to attack Sherburn with over 500 men. Not knowing that this was an exaggeration, Sherburn re-embarked his men, but found out the next day that Butterfield was still holding out, and set off again for The Cedars.
Again, however, his approach was discovered and about four miles (6km) from The Cedars he was attacked by Lorimier's men. Believing himself outnumbered, Sherburn surrendered with 97 of his men. Casualties had been light on both sides, but unfortunately the one death on the British side was a Seneca war chief, whose demise caused the tribesmen to threaten their prisoners.7
Having captured Butterfield's and Sherburn's commands (487 men in all) Forster placed the officers in the custody of some priests and set out for Montreal Island with 500 men and the rest of the prisoners. On 24 May, he arrived at Pointe Claire, 18 miles (29km) from Montreal, and learned that Arnold was entrenched around a large stone house at Lachine, with 600 men and some artillery. In fact, Arnold was also expecting the 1st Pennsylvania Battalion and some other detachments, which would eventually give him 1,500 men. Whilst his force grew, Forster's shrank as the independent-minded tribesmen returned home with their plunder. With no further news from Carleton, Forster decided to pull back to The Cedars, but was embarrassed by the numbers of prisoners and decided to effect an exchange. He found Sherburn and Butterfield so eager to remove their men from the clutches of the Indians that not only did they agree to leave four captains as hostages and that no prisoner would serve again during the war, but also that no similar condition would apply to the British prisoners.
As Forster pulled back, Arnold moved up to the eastern end of Montreal Island and on 26 May arrived at Vaudreuil by bateaux. Seeing Forster's men drawn up for battle, Arnold kept out of range of the two cannon Forster had captured at The Cedars. Landing on the opposite bank, Arnold formulated a plan to cross the river at night and attack Forster's flank and rear at dawn. However, his officers - especially Hazen - felt that the Indians would prevent any surprise and that a night march would end in confusion. The acrimonious discussions ended just after midnight and at 2.00am Sherburn arrived under a flag of truce and outlined the response to Arnold's threat to kill any Indian he caught serving with Forster and burn their villages. Arnold knew that any prisoner in their hands would be tortured and killed and agreed to the terms negotiated with Forster (except for the condition on not serving again during the war). It is worth noting that there was no mention of any ill-treatment of the men held by Forster.
The transfer occurred between 27 and 30 May, after which Forster retired to Oswegatchie and de Haas (who had taken over from Arnold) withdrew to Lachine. De Haas ignored an order from Arnold to burn the village of Conosadaga, believing that it would serve no purpose and might unleash forces that he had insufficient force to confront, let alone control. As the prisoners returned south, Congress condemned the actions of Butterfield and Arnold. Using the alleged atrocities as an excuse, they repudiated the agreement, despite written confirmation by one of the four hostages that the allegations of brutality were untrue.
