Brittany is nearing 30, living in New York and having a quarter life crisis. No job, no man or woman, overweight, she is convinced by her doctor to improve her health. She starts small and finds a local runners group where she meet two misfits just like her. They train for marathon (hero's quest), have a crisis of confidence (RomCom snafu 30 minutes before the end) and ... well, you can guess the rest.
Along the way to make some money she discovers house and dog sitting which leads her to her romantic interest Jern ( a very Aziz Ansari character). More classic RomCom tropes emerge.
My guess is that this played so well at Sundance because it looks like an indie film with no-name actors but at heart is a classic studio story with a big name producer behind it (Tobey Maguire).
* * * of 5