Gwen 10 is a Season 2 episode of the series, Ben 10.
When Ben wakes up in the morning, he finds That Gwen is in danger because 2 Thieves bump into her and scared her, and as usual, Ben tries to go "Hero mode" but....Something unusual happened, Ben's Omnitrix is not in his arm! He really doesn't understand, and after Grandpa Max helps Ben, Ben comes into the Rustbucket again, He asks Gwen to help Ben finding his Omnitrix, But Gwen asks back "What does it looks like?" Ben really doesn't understand, His Grandpa said just to relax. then When Ben is on the way, he discovers that he is back in time, to the first day on the summer vacation, on the place he founds the omnitrix. But Still, Grandpa Max and Gwen doesn't understand what Ben's Talking about.
When Ben Sees the meteor that brings Omnitrix, he goes to the place where the Omnitrix crashed before, but when he is there already, he finds Gwen found it first!! Gwen looks she is wearing the Omnitrix, and Ben seems really mad, Gwen accidentally transforms into Heatblast, but the female version. Ben said that what Gwen's is doing with Heatblast (making fireworks that shaped "Gwen" in the sky) needs a month to master it, after the night, they go into the bowling field, Ben found that Gwen seems better controlled with the Omnitrix on the first time, and Ben doesn't like it. But Vilgax found them, Vilgax is not injured at that time, and he brings Gwen inside the ship.
The story is like the same as the episode "And Then There Were 10". but a little changed like Vilgax is not injured, The aliens turns female, and the Story changed into "Gwen" styles. The story ended with Grandpa Max is wearing the Omnitrix and transforms into Upgrade, like what Ben says. and Vilgax defeated, and This episode is one of the "What if?" Episode, the story ended when it shows the comic form of Ben 10.