Again he joined the Earl of Cumberland in 1591 on an expedition directed against Spain, off the coasts of which he successfully took two caravels by one of the stratagems for which he was famous. He had boarded one from the ship’s boat; he manned her with a part of his boat’s crew, and rowed back to his ship. The Spaniards on the other caravel far in the distance thought that the first, her consort, had been dismissed, and so shortened sail to meet her; and was consequently taken unawares by a mere handful of men. But Monson only wanted to obtain information as to the enemy, and let them both off. This act turned out fortunately for him; for shortly afterwards, being left in charge of a prize taken from the Dutch, he was attacked by the Spaniards in six galleys, the consequence being that he was taken prisoner, when he found that his recent conduct towards the caravels had been reported favourably, and he was treated with more courtesy than had been usual before. But he was to suffer a long captivity for all that. At the Tagus he would probably have escaped had not an unforeseen chance prevented. While the galleys were in the harbour, a Brazilian, master of a Dutch ship, chanced to come on board that on which Monson was confined, and, pitying his hard fate, offered to take him off on his vessel, if he could devise any plan which should not implicate himself. Monson gave out to the rest of the prisoners that, tired of his life, he intended to drown himself. His intention really was to drop quietly into the water, and if possible swim to the friendly bark. But just before he had made his arrangements, the galleys were ordered to sea, and when they returned the ship had sailed. It is probably fortunate for him that he did not make the attempt, as, had it been frustrated, he would have probably suffered death, as did an Italian a short time afterwards, who had been trying to raise a general conspiracy on board. His execution was effected in the most horrible manner, his arms and legs being severally tied to the sterns of four galleys, which were rowed in four different directions, thus quartering him.