Sift Heads World Act 3: Alonzo's Reinforcement is the continuation of Sift Heads World: Act 2: The Treacherous Return.
After "The Treacherous Return" events, Vinnie and his team came back to Chicago and go for a stroll in his GT-500. While they were talking, suddenly a truck hit the car and they were all injured.
Vinnie (or Kiro and Shorty, based on the character you used, but I think the Protagonist in this act is Vinnie) got out of the car to kill the Alonzo's henchmen, Vinnie got arrested by the cops.
That was a trap setted by Alonzo and the Commissioner.
After a while, Kiro and Shorty (or Shorty and Vinnie if you choose Kiro, Vinnie and Kiro if you choose Shorty) wears cop clothes and rescue Vinnie.
After being rescued, Vinnie thought that the justice system has been corruped, decided to go to ask the Mayor. The cops still in searching for him, so he sneaked in with a tranquilizer gun.
When the Mayor met Vinnie, he said he already know about Alonzo, ask Vinnie to find the one who took a hand on helping Alonzo.
Vinnie went to the Crime Hideout, killed all the guards there and got a disk. He turned the computer on and placed the disk in there, discovered that the Commissioner was the one behinds this. But he thought that wasn't enough, so he went to the Business Tower and took a picture of the Commissioner was leaving the Crime Hideout.
Still, the Mayor said that he needed more details about that, so Vinnie went to Palermo, Italy to get more information since Alonzo's Hideout was around there.
In the hotel, Vinnie took down all of the guards there and got the information.
In the apart block, Vinnie took down all of the guards there and got the information.
In the port, Vinnie took down all of the guards there and got the information.
After got all of three information, Vinnie went back to Chicago and went to the City Hall to talk with the Mayor. But the Mayor was out, called Vinnie to meet him in the Gigi Restaurant in one hour. Vinnie went there, and talk to him. Unfortunately, Alonzo's henchmen came in and kill the Mayor, so Vinnie defended himself. One of them survived, and Vinnie tortured him to get the info where was Alonzo's hideout. The henchmen told him that Alonzo was hiding in a secret passage in the bar.
Vinnie went to the bar and found the secret passage in the toilet. He went in and killed all the guards there, then met Alonzo with three tough guards. Vinnie killed all the three tough guards and chase Alonzo.
Alonzo used a machine gun to defend himself from Vinnie. But he failed to survive from the legendary bounty hunter, got injured. But Vinnie decided to arrest Alonzo in their jail instead of killing him.