By June of 1828, Joseph Smith and Martin Harris had translated 116 pages from the portion of the gold plates known as the Book of Lehi. Harris had then asked Smith's permission to bring their manuscript-in-progress back home with him to Palmyra to build support among friends and to finally convince his doubting wife that their work was legitimate. Smith asked Jesus about this and the answer was no.
But Harris persisted in asking. Knowing that Harris was the only man who could finance the publishing of the work, Smith inquired a second and then a third time, and finally Jesus granted permission so long as Harris only showed the work to four or five family members. Soon after Harris departed, Smith and his wife Emma's first child was born, a son they named Alvin. But it was a difficult delivery that nearly killed Emma, and the child died the same day he was born.
When Harris had been gone three weeks, Emma encouraged Joseph to go Palmyra to check on him. At his parents' house, Smith met up with Harris and could tell from his expression that something had gone wrong. "Martin, have you lost the manuscript?" asked Smith. "Yes, it is gone," said Harris. "I know not where." "Oh, my God!" said Smith, "All is lost! All is lost! What shall I do? It is I who sinned by allowing this to happen."
Jesus later revealed to Smith that Satan had inspired wicked men to steal the manuscript so they could discredit him by pointing out the all the discrepancies when he retranslated the Book of Lehi. Aware of this evil plot 2,300 years in advance, however, Jesus had told Lehi's son Nephi to write a second account of the events covered in the Book of Lehi, and so Jesus told Smith to use this other account to replace the lost 116 pages.
The gold plates and the Urim and Thummim—which had been taken away when the manuscript was lost—were returned to the repentant Joseph Smith by the angel Moroni at the end of 1829 along with the promise of a new scribe to assist in the translation. In the meantime, during the winter of 1828-1829, Emma acted as a temporary scribe as Smith continued his translation with the Book of Mosiah.