When do I get dual weilding?

[Democratic skeletor]

I got past the demo level and killed the mothman, also did the 2 side mission as well, but I still dont have the ability. Can someone tell me if this is a bug or intentional, thanks

[G_Medlin]

You'll come to a point where you need to inject yourself with a solution that enables duel-wielding! Head for the Patriarch.