Shortly afterwards, one of these ships, the _Lissa_, put into Emden with a rich Swedish prize. Lying in the harbour was an English man-of-war, and the captain of this ship, declaring that the English sailors on board the _Lissa_ were all either deserters or men who had bound themselves to serve in the British Navy, required that they should be given up to him. As compliance was refused, he went on board the _Lissa_ with an armed escort, and, disregarding all the protests of its captain, took away with him twenty-six members of the crew. This action was regarded by Frederick as an infraction of Prussian rights of sovereignty, and representations to that effect were made in London before it was discovered in how irregular a manner the _Lissa_ had become possessed of her papers. The matter was then discreetly allowed to drop. The Swedes, for their part, contested the legality of the capture, but the Prussian Government ruled that the letter of marque was valid, although it had not actually been issued by royal authority. At the same time Prussia advanced the strange view that, in the event of the owners of the _Lissa_ having had cognizance of the deception which had been practised, King Frederick was entitled to the whole value of the prize. Instructions were, however, given that the _Lissa_ should be deprived of her charter, but before they could be executed she had sailed for England. Another of Douglas's privateersmen, the _Prince Ferdinand_, under a Captain Merryfield, had betaken herself to the Mediterranean, where, in a nine-months' cruise, she captured thirteen prizes, but caused so much confusion that the King thought it wiser to put a stop to the whole undertaking. The immediate ground for this step was the complaints of the Ottoman Government, with which Frederick was negotiating with a view to obtaining its support in the prosecution of the war. The appropriation of a couple of female negro slaves belonging to a pasha, who were on board one of the ships captured by Merryfield, seems to have had at least as much weight in the Turkish grievance as the more substantial losses of the merchants of Salonika. As Prussia had no territory and very little diplomatic representation on the shores of the Mediterranean, Merryfield was obliged to take his prizes into neutral harbours and place them in the custody of the English Consuls. They were the subjects of endless law suits, tedious international wrangling, and practically no profits. Merryfield's wild career was terminated by a charge of secretly selling neutral goods from one of his prizes to his own advantage. At the instance of the Prussian Government he was flung into gaol at Malta. He remained in prison five years, and even at the end of that term would not have regained his liberty if the Grand Master of the Maltese Knights had not refused to pay for his maintenance any longer.