LDS History, Aug 20, 1842

-- Aug 20, 1842
Elder Orson Pratt is excommunicated for refusing to accept the doctrine of plural marriage. (1)

Nauvoo, Illinois. Joseph Smith had a meeting with his brother Hyrum Smith and four others where they discussed the illegal proceedings of their prosecutors. (2)

[Quorum of the Twelve] Orson Pratt excommunicated. Amasa M. Lyman ordained. (3)

-- Aug 24, 1842
Nauvoo, Illinois. Thomas Carlin, governor of Illinois, sent a letter to the Prophets wife, Emma Smith, assuring her that all of his actions concerning Joseph Smith had been prompted by a strict sense of duty. (2)

-- Aug 26, 1842
Nauvoo, Illinois. Joseph Smith had a meeting with the Twelve in which he stressed the importance of continued missionary work, despite the persecutions against the Church. (2)

-- Aug 29, 1842
Nauvoo, Illinois. Joseph Smith gave a talk in which he promised the Saints that there would be no lives lost if they would listen to his counsel. (2)

-- Aug 31, 1842
Nauvoo, Illinois. Joseph Smith rode to a grove near the Nauvoo Temple with his wife, Emma Smith, to attend a meeting of the Relief Society. (2)

-- During 1842 Aug
[Lucy Mack Smith] Joseph goes into hiding. (4)

-- Sep 1, 1842 & 6
Joseph Smith writes two letters to the church regarding baptism for the dead, clarifying the doctrine and practice. (D&C 127, 128) (1)

-- Sep 1, 1842
Nauvoo, Illinois. While in seclusion, Joseph Smith wrote a general epistle to the Church concerning the work of baptisms for the dead, which was later canonized as Doctrine & Covenants 127. (2)

-- Sep 2, 1842
Nauvoo, Illinois. Joseph Smith received a report that the sheriff was on his way to Nauvoo with a posse. (2)

-- Sep 3, 1842
Nauvoo, Illinois. Joseph Smith escaped out the back door of his home from Deputy Sheriff Pitman and others who had come to arrest him. (2)

-- Sep 6, 1842
Nauvoo, Illinois. Joseph Smith wrote a letter to the Church containing further instruction concerning baptisms for the dead, which was later canonized as Doctrine & Covenants 128. (2)


Footnotes:
1 - Wikipedia, 19th Century (Mormonism), http://en.wikipedia.org/wiki/19th_century_(Mormonism)
2 - BYU Studies Journal, volume 46, no. 4: A Chronology of the Life of Joseph Smith
3 - Wikipedia, Chronology of the Quorum of the Twelve Apostles (LDS Church), http://en.wikipedia.org/wiki/Chronology_of_the_Quorum_of_the_Twelve_Apostles_(LDS_Church)
4 - Proctor, Scott and Maurine Jensen, editors, History of Joseph Smith by His Mother: Revised and Enhanced
Mormon History Timeline /Chronology
http://lds-church-history.blogspot.com/