The town had been abandoned, on his approach, and on the 28th he advanced and invested Crom Castle, on the eastern side. By the 30th he had carried the outer works, and driven the enemy within the walls, though not without considerable loss, and at once opened a cannonade upon the castle. While here, he received word that Colonel Berry was advancing on him by way of Lisnaskea, with eight hundred regulars, followed by the united forces of Wolseley and Hamilton. Without discontinuing the operations against the fort, he withdrew a part of his command about two miles to the eastward, and took post at Newtownbutler. Learning that the enemy's forces had all united, and were too powerful to meet in the open country, he sent Colonel Anthony Hamilton, with O'Brien's regiment of dragoons, to hold them in check, while he himself prepared for a retrograde movement to Belturbet. The troops of Hamilton were drawn into an ambush by Berry, near Lisnaskea; their commander was wounded, his next in command killed, and in a retreat which was ordered, two hundred and thirty were slain or taken prisoners. Mountcashel, on hearing of this disaster, advanced with his own regiment of horse; arrested the retreat and repulsed Berry; but seeing Wolseley, with a force of 8,000 men, close in Berry's rear, he took up his retreat to Belturbet. Berry and Wolseley moved forward rapidly; Mountcashel closely pressed, and considering resistance safer than flight, at last drew up his men about a mile to the south of Newtownbutler, and hastily formed in line of battle. The action which ensued was disastrous to the Irish army. Opposed by more than double their number, and attacked in front and flank, they fought with great bravery, and the battle might have resulted in their favor, but an unfortunate blunder, in carrying out the general's orders, disarranged their lines, created a panic among the soldiers, and a total rout was the consequence. The lake and its tributaries cut them off from escape in any direction, and, being completely hemmed in, they were slaughtered without mercy. Their loss is estimated to be over 2,000 men, of whom 400 only were killed in the battle, the rest being massacred through the night, to the cry of "No popery!" or drowned in the lake into which they had thrown themselves in the vain hope of escaping the general carnage. Mountcashel himself was wounded and taken prisoner, but was saved from death by a captain named Cooper, to whom he had previously rendered a similar service. Sir Stephen Martin and Lord Abercorn, and many officers of distinction, were killed. All that escaped of this unfortunate command fled towards Belturbet, and, after the capture of their general, the expedition was abandoned.