After completing The Deserters 2, The Black Shield 3, and Suspicious Hoofprints, Vimes opens up the conclusion of the quest chain starting in patch 2.3.0:
Krog in Brackenwall Village in the Dustwallow Marsh is said to be investigating the burning of the Shady Rest Inn. Located on the border of the Barrens and Dustwallow Marsh, the inn was torched by unknown vandals. Although the owner of the inn, a man now known as Smiling Jim, escaped, his wife and child were not so lucky. Their brutal deaths weakened Jim's grip on sanity, and he can now be found in the city of Theramore, reciting the same poem over and over again.
Very scant evidence is available to indicate who or what was responsible for the destruction of the inn. Still, some adventurers have reported seeing a set of hooftracks leading away from the inn, and at least one investigator recovered a scorched black shield from the wall of the inn. According to the engraving on the shield, it was crafted by Mosarn — a very respected blacksmith in Thunder Bluff. Even more importantly, a golden badge belonging to Lieutenant Paval Reethe, a deserter from the Theramore Isle military, has been found in the charred ruins of the inn. With the help of an ogre named Ogrok, Paval Reethe was tracked down, but he was executed by the Theramore military before he could disclose the name of the person responsible for the arson.
Although many adventurers have contacted Mosarn regarding the shield, he was unable to provide any specific information regarding its owner or anything that may help the investigation. Thus, it can be concluded that the investigation has reached a dead end and is unlikely to advance until either Mosarn provides the information required or some additional clues surface.
The burning of the Shady Rest Inn was an unfortunate incident that spelled trouble for the relationships between the Alliance and the Horde. The fact that Thrall specifically ordered the humans of Theramore Isle to be left alone further fuelled the Warchief's anger over the destruction of the inn, leading him to order an investigation into the incident to find those responsible and bring them to justice.
Patch 2.3.0 added a concluding chapter to this story. After completing Black Shield 5, Suspicious Hoofprints, and Questioning Reethe, Mosarn will volunteer new information to the player and give the quest "Return to Krog". This begins the final steps of the quest chain.