The story of Zeniff actually begins back in Omni 1:27–30, where Amaleki mentioned two expeditions to the land of Lehi-Nephi and added that he had a brother who went, presumably with the second party. Amaleki had not heard anything about the second group since then. His entire record is two short chapters long.
There actually were two trips or expeditions of Nephites to the land of Lehi-Nephi, which at the time was occupied by Lamanites. Zeniff first recorded the surprising events that transpired during the first of these expeditions. As their group got close to the land of Nephi, Zeniff was sent to scout out the situation so that their army could "destroy" the Lamanites (9:1). Zeniff was chosen for this mission because he was prepared. He had done his homework: (1) he knew the language, and (2) knew the land. When he "saw that which was good among [the Lamanites]," he recommended that they make a treaty with the Lamanites rather than try to conquer them. But the leader of this trip was "stiffnecked" and contentious, which caused a fight and bloodshed among the expeditioners. All but fifty were slain. The survivors, including Zeniff, returned home to Zarahemla.
Zeniff, "being over-zealous to inherit the land of [his] fathers," set out on a second expedition to the land of Lehi-Nephi. This group suffered "famine" and "sore affliction," recognizing that the problems were rooted in their behavior, "for we were slow to remember the Lord our God" (9:3). Zeniff then led a small delegation with four men from his group to meet with the king of the Lamanites to see if they could "possess the land in peace" (9:5). Preferring peace, and as he had recommended making a treaty before, Zeniff went to the king who agreed and even moved his people out of that area. Trusting the king, Zeniff and his people were given the lands of Lehi-Nephi and Shilom, and they began to repair walls, build buildings and plant crops, not realizing that the Lamanite king had designs to put them into bondage or oppressive servitude (9:10).