"Yes. And that's why I know you'll kill him. You're better than him."
An alliance between the UED and the Confederate Resistance Forces raided Boralis, Braxis, gaining access to Arcturus Mengsk's guarded files, such as his travel schedule. The Confederates used this information to plan an assassination attempt on Mengsk. The assault force would be led by Captain Angelina Emillian, Mengsk's former military trainer. Samir Duran said he was confident that Emillian would win because of that, but also warned her she couldn't expect to be rescued if she didn't succeed in killing Mengsk.
Arcturus Mengsk made his first visit to Umoja as emperor of the Terran Dominion, and also to visit his son, Valerian. He took a fleet of capital vessels commanded by General Edmund Duke with him. However, Umojan ambassador Ailin Pasteur wouldn't allow the vessels to approach beyond the outer shipping markers; Mengsk had to descend in an obsolete gun cutter early in the morning. He only took approximately 12 soldiers with him and two Wraiths.
While Mengsk was visiting Pasteur's home, he was in a temporarily vulnerable position, which was when the Confederate Resistance Forces struck. They used a Cassandra scrambler to cut off communications with Mengsk's fleet and the local Umojan Protectorate forces. Their Wraiths heavily damaged the cutter, causing it to fall into a landing shaft and preventing it from flying, as well as strafing the area and destroying the Dominion Wraiths. A Confederate heavy lander also descended, disgorging approximately 30 marines led by Captain Angelina Emillian.
Mengsk, his son Valerian and the warrior Master Miyamoto fled underground to the shaft, pursued by Confederate marines. Arcturus Mengsk entered the cutter, using its weapons to fight back and its powerful communications equipment to contact General Duke. Meanwhile, Valerian and Miyamoto held off the Confederates as long as they could, until Captain Emillian arrived and shot Miyamoto down.
Valerian tried to surrender to her, but she hated the Mengsk family and prepared to kill him. As she explained her reasons, Miyamoto used the last of his strength to disable her weapon, enabling Valerian to shoot her down. As she bled to death, she told Arcturus Mengsk that "the UED are going to clean your clock but good." However, Mengsk didn't know who the UED were yet.
The ground battle continued for a short time until Duke's fleet arrived, destroying the remaining Confederate soldiers. He had ignored Umojan instructions to stay away as soon as the communications scrambling started. The Umojans once again had to negotiate Dominion vessels away from their planet.