As members of the Royal Guards, Special Investigation Unit follow agents Marcus and Mikal as they go undercover to solve crimes against the country of Xylandria. This special unit was formed by King Wilfred when unsolved major crimes started rising. In Unity Bridge, someone keeps burning down the wooden pillars that are to be used to hold up the bridge crossing the Oklib River. King Wilfred promised the citizens of the newly annexed country of Zanderland that he would build the bridge to connect the two countries into one. Marcus and Mikal, with the help of some of their fellow agents, are assigned to solve this mystery of who is sabotaging the bridge and why.

While undercover, they pose as traveling vendors. Marcus sharpens knives, farm implements, and just about anything that requires a sharp edge. Mikal sells a variety of knives as his cover. They set up their booth in the makeshift marketplace in the town of Molenzia. From their temporary headquarters, they work on who and why someone is sabotaging the bridge. They have help from other agents that are known to them and some others who are not.

Watch for further adventures of Marcus, Mikal, and the Royal Guard Special Investigation Unit as they solve crimes throughout the kingdom of Xylandria.