The Wall Rose invasion was a crisis that began when the Beast Titan turned the Ragako inhabitants into mindless Titans to wander throughout Wall Rose. Eren Yeager was nearly captured by the Colossus and Armored Titans, though through the combined efforts of the military he was retrieved and Wall Rose was cleared of all Titans.
Prelude: In the aftermath of the 57th Expedition Outside the Walls, the Survey Corps was summoned to Mitras in order to hand Eren Yeager over to the Military Police Brigade as per the agreement made during Eren's trial a month prior. However, Commander Erwin Smith devised a secret mission for the Survey Corps to confront and capture Annie Leonhart, a former trainee of the 104th Training Corps suspected of being the Female Titan which sabotaged the 57th Expedition. This operation would commence in Stohess District, Annie's stationing as a recruit in the Military Police and the half-way point between Karanes District and Mitras.
The Invasion: Sometime around the expedition, Wall Rose was infiltrated by Zeke Yeager, the Warchief of Marley's Warriors, accompanied by Pieck and a few other Marleyan soldiers, unbeknownst to everyone in the wall. Sometime after this infiltration, they made their way to the village of Ragako in the southwestern region of Wall Rose. There, the soldiers prepared a gas imbued with Zeke's spinal fluid, and released it into the village, paralyzing the villagers and marking them with a coordinate.
Sighting and evacuation: Sometime around the expedition, Wall Rose was infiltrated by Zeke Yeager, the Warchief of Marley's Warriors, accompanied by Pieck and a few other Marleyan soldiers, unbeknownst to everyone in the wall. Sometime after this infiltration, they made their way to the village of Ragako in the southwestern region of Wall Rose. There, the soldiers prepared a gas imbued with Zeke's spinal fluid, and released it into the village, paralyzing the villagers and marking them with a coordinate.
Utgard Castle: Upon arriving at Utgard Castle over eleven hours after the sighting, the south and west teams discovered that the castle had been inhabited by an unknown individual or group. Various supplies had been left in the castle, with labels marked in an unknown writing. The recruits discussed the events of that day, and Connie mentioned the Titan that was found in his house, noting how it resembled his mother.
Source: Wall Rose invasion, available under CC BY-SA 3.0.