Mainland affairs
A civil war was raging in the Kingdom of Jerusalem between two rival factions: the Templars, Venetians, and Pisans against the Hospitallers, Genoese, and Catalans. The Ibelin-led government had sided with the Genoese, but when the tide turned against them in late 1257, the government had to change sides; to do this without losing face, they decided to again invite the next-in-line to the throne to take charge as regent. John of Jaffa and the master of the Temple, Thomas Berard, urged Bohemond VI of Antioch to bring Plaisance and her son to Acre, the kingdom's capital.
Plaisance sailed with Hugh from Cyprus to Tripoli, where she met with Bohemond. Mother and son arrived in Acre on 1 February 1258, escorted by her brother. At a session of the High Court, Bohemond urged that Hugh be acknowledged as King Conrad's heir and lord of the kingdom in the absence of the king and that Plaisance be recognized as Hugh's bailli. The Templars, the Teutonic Knights, most of the barons, and the Venetian and Pisan delegates swore fealty to Hugh, but the Hospitallers and their allies insisted that nothing could be decided in Conrad's absence. Plaisance was elected bailli by a majority vote and her father-in-law, John of Arsuf, duly resigned the bailliage to her. She was only distantly related to Conrad and received the regency on account of her relationship to her son.
As soon as Plaisance took up the government of the Kingdom of Jerusalem, she and her brother launched a determined attack on the Genoese in Acre. She ordered all crown vassals to abandon the Genoese, whom Bohemond tried to starve out, and to support the Venetians. John of Arsuf and his son Balian, Plaisance's estranged husband, then reconciled with Plaisance and Bohemond. They agreed to the annulment of Plaisance and Balian's marriage and in return Plaisance appointed John as her bailli. He was instructed to sternly deal with the rebels. Plaisance and her son withdrew with her brother to Tripoli, from where they returned to Cyprus. Plaisance's regency was made effective by Bohemond's military assistance: he provided 800 men-at-arms to force the Genoese and their allies to cease fighting in Acre, though without success. The Venetians soon triumphed nevertheless.
In 1258, Pope Alexander granted Plaisance's request and annulled her marriage with Balian of Arsuf. His father, John, died soon after his reappointment to the bailliage and Plaisance returned to Acre on 1 May 1259 to install Geoffrey of Sergines, seneschal of Jerusalem, as her new bailli. The Latin patriarch of Jerusalem, James Pantaleon, supported Plaisance's regime on the mainland. At some point Plaisance entered into a sexual relationship with John of Jaffa. He was a married man, and their affair may have become common knowledge by early 1261. Pantaleon, who became Pope Urban IV on 29 August, chastisised Plaisance for the relationship in a letter. Plaisance died on 22 or 27 September 1261. Urban IV could not have been aware until at least late October, and the letter may not have been finished. She was succeeded as regent by her cousin Hugh of Antioch.