When you’ve got a movie about a guy pinned by a massive boulder until he decides to chop his arm off, you wouldn’t think there’s room for much of a supporting cast. But at the Hot Tub Time Machine junket this weekend, Lizzy Caplan assured me there’s a little more to it. Danny Boyle is directing the film based on the true story of a rock climber named Aron Ralston. After five days of being stuck between a giant rock and canyon wall, he opted to do the unthinkable and remove the appendage keeping him from freedom.

As you would expect, resorting to such a drastic measure messes with your head. Caplan explained, “Most of the movie is James Franco stuck in a cave, but he has hallucinations so there are other characters besides himself and a boulder.” Her character is Franco’s sister. There’s also Kate Mara and Amber Tamblyn who will be playing hikers he meets before the accident.

Clearly Franco is the core of 127 Hours, but the whole hallucination idea can take what seems to be a limited plot into a variety of different directions. In terms of Caplan’s casting, I couldn’t be happier. She’s been able to accomplish a lot from the supporting character’s perspective in films like Mean Girls and Cloverfield, so will likely do the same here. However, I think it’s time she’s given a starring opportunity.