In 2369 the HIv SuH was ordered to the Velexian system to represent the Klingon Empire in peace talks with the Hidran people. During these talks the Hidran Ambassador, Zhad, died after consuming what appeared to be grain but was actually nano machines that rejected Zhad's breathing mask, and Lieutenant Commander Data was damaged after swallowing this same grain.
As a result of these unforseen developments the talks nearly failed, however Captain Jean-Luc Picard was able to convince both Kadar and the Hidran Captain Urosk to put aside their differences and help him stop Data from attacking Qo'noS.
After Data was stopped and treated for his condition, Kadar departed for Klingon territory, but promised Picard that he would ensure that the Klingons would honor their new treaty with the Hidrans. (TNG novel: Foreign Foes)