Mosiah 21:26 - 21:30

Mosiah 21:26 Nevertheless, they did find a land which had been peopled; yea, a land which was covered with dry bones; yea, a land which had been peopled and which had been destroyed; and they, having supposed it to be the land of Zarahemla, returned to the land of Nephi, having arrived in the borders of the land not many days before the coming of Ammon.

These scouts did not find Zarahemla but did stumble on a land that was covered with the bones of thousands of dead people which they supposed to be all that remained of Zarahemla. In fact this party which brought this bad news had just arrived back in town not many days previous.
[Thinking that Zarahemla was indeed destroyed probably made the Limhi’s people think they were all that was left of the Nephite civilization and no help was available to free them from their slavery to the Lamanites. So one can imagine the emotion among Limhi’s people when Ammon tells them where they were from, that the Nephites still exists and that they are not the last of their people.]

Mosiah 21:27 And they brought a record with them, even a record of the people whose bones they had found; and it was engraven on plates of ore.

These scouts found among the bones a record, which they suppose to be a record of this fallen people and their history, which were written on metal plates.

Mosiah 21:28 And now Limhi was again filled with joy on learning from the mouth of Ammon that king Mosiah had a gift from God, whereby he could interpret such engravings; yea, and Ammon also did rejoice.

Limhi was thrilled to know that there was someone who had the gift of God who could interpret the language on these plates. Limhi really wanted to know what had brought about the destruction of these people that this scouts had discovered. Ammon, himself, was just as anxious to have them interpreted as was Limhi.
[This all could be compared to the desire to be able to translate ancient Egyptian, Mayan and other such languages of civilizations that no longer exist. We are just as curious as to what happened to them and why they no longer exist.]

Mosiah 21:29 Yet Ammon and his brethren were filled with sorrow because so many of their brethren had been slain;

In addition, Ammon was also sad to hear of the troubles of the people of Limhi and the great loss of life because of warfare with the Lamanites.

Mosiah 21:30 And also that king Noah and his priests had caused the people to commit so many sins and iniquities against God; and they also did mourn for the death of Abinadi; and also for the departure of Alma and the people that went with him, who had formed a church of God through the strength and power of God, and faith on the words which had been spoken by Abinadi.

They were sadden to hear that is was because of the great iniquity of the previous king which influenced the people to become the same way. Ammon also learned about execution of a prophet named Abinadi and the escape of Alma and some of the people from the clutches of king Noah and who had formed a church because of the preaching of this prophet Abinadi.