Saltø is a manor house and estate located 8 kilometres (5.0 mi) west of Næstved in southeastern Denmark.

Shortly thereafter, possibly already the same year, he sold it to his brother-in-law, Corfitz Ulfeldt, who then served as Steward of the Realm.

[2] After living for a time in concealment at Amsterdam, Ulfeldt moved to Stralsund in Swedish Pomerania.

He persuaded the commandant of Nakskov (a strategically crucial fortress) to surrender to Charles X, and did his best to convince his countrymen that resistance was useless.

He even loaned the Swedish king a fortune to finance the war with money that, it is believed, was embezzled from the Danish state.

Finally, as one of the Swedish negotiators at the Treaty of Taastrup, he was instrumental in assuring the humiliation of his native land.

[3][2] Ulfeldt's treason was rewarded by Charles X of Sweden with ennoblement as the Count of Sölvesborg in Blekinge and he was in the same time given his Danish holdings back.

He later returned to Copenhagen to try to make his peace with his lawful sovereign, who promptly imprisoned him and his wife.

Plessen had close ties to Frederik IV's brother, Prince Carl, and was a member of the government (Gehejmekonseillet) from 1730.

His other estates included Førslevgaard, Harrestedgård, Gunderslevholm, Kastrupgård, Fuglebjerggaard, Fodbygaard and Dronningelund.

He was known for his many initiatives to improve the living conditions for the peasants on his estates, for instance by establishing numerous schools.

Frederik Christian von Plessen, who had no children, in 1763, ceded his estates to the four grand-nephews of the other line.