She plays Carol, daughter to a voice-over-industry legend (Fred Melamed), one of several male basso profundos vying to replace the late, legendary Don LaFontaine (the actual "in a world" guy) as the go-to voice for blockbuster entertainment.
Bell has written the voice-over business as a microcosm of Big Hollywood, and it's a funny joke. Carol's fat, bald, 50-something father has groupies and an impossibly young girlfriend. He's vain and entitled and touchy. So is his rival (Ken Marino).
Carol has followed her famous dad into the fringes of the business. She's a vocal coach and is called in to help famous actresses (funny cameo for Eva Longoria) through accent emergencies.
She happens to be in a studio when an emergency voice-over job for an animated movie opens up, so she takes it. When the movie becomes a hit, so does Carol, suddenly pushed to the front rank of possible LaFontaine successors.
The movie is feather light, but it's also sneakily relevant and timely. Bell realizes that Hollywood itself is changing. Its most loyal audience is increasingly female, and she makes the point that its male leadership is slow to react.
Bell takes the idea that women need to be heard, need to have a voice, and makes it a joke with literal and figurative implications. She's given these implications much thought and embellishes the idea with some choice bits.
In a world where women direct themselves, which is to say Bell's world, she's uncommonly generous. There are large supporting roles for Rob Corddry, Michaela Watkins and Demetri Martin.
A few of Bell's closest celebrity friends pop up in the epilogue, where we get an eyeful (and earful) of the blockbuster trailer of the near future.