On the 25th of May, 1585, at an hour after midnight, he had a secret interview with Count Meurs, stadholder for the States of Gelderland, and agreed to transfer his mercenary allegiance to the republic.  He made good terms.  He was to be lieutenant-governor of Gelderland, and he was to have rank as marshal of the camp in the States’ army, with a salary of twelve hundred and fifty guilders a month.  He agreed to resign his famous castle of Blyenbeek, but was to be reimbursed with estates in Holland and Zeeland, of the annual value of four thousand florins.

After this treaty, Martin and his free lances served the States faithfully, and became sworn foes to Parma and the King.  He gave and took no quarter, and his men, if captured, “paid their ransom with their heads.”  He ceased to be the scourge of Gelderland, but he became the terror of the electorate.  Early in 1586, accompanied by Herman Kloet, the young and daring Dutch commandant of Neusz, he had swept down into the Westphalian country, at the head of five hundred foot and five hundred horse.  On the 18th of March he captured the city of Werll by a neat stratagem.  The citizens, hemmed in on all sides by marauders, were in want of many necessaries of life, among other things, of salt.  Martin had, from time to time, sent some of his soldiers into the place, disguised as boors from the neighbourhood, and carrying bags of that article.  A pacific trading intercourse had thus been established between the burghers within and the banditti without the gates.  Agreeable relations were formed within the walls, and a party of townsmen had agreed to cooperate with the followers of Schenk.  One morning a train of waggons laden with soldiers neatly covered with salt, made their appearance at the gate.  At the same time a fire broke out most opportunely within the town.  The citizens busily employed themselves in extinguishing the flames.  The salted soldiers, after passing through the gateway, sprang from the waggons, and mastered the watch.  The town was. carried at a blow.  Some of the inhabitants were massacred as a warning to the rest; others were taken prisoners and held for ransom; a few, more fortunate, made their escape to the citadel.  That fortress was stormed in vain, but the city was thoroughly sacked.  Every house was rifled of its contents.  Meantime Haultepenne collected a force of nearly four thousand men, boors, citizens, and soldiers, and came to besiege Schenk in the town, while, at the same time, attacks were made upon him from the castle.  It was impossible for him to hold the city, but he had completely robbed it of every thing valuable.  Accordingly he loaded a train of waggons with his booty, took with him thirty of the magistrates as hostages, with other wealthy citizens, and marching in good order against Haultepenne, completely routed him, killing a number variously estimated at from five hundred to two thousand, and effected his retreat, desperately wounded in the thigh, but triumphant, and laden with the spoils to Venlo on the Meuse, of which city he was governor.