Andrea Riseborough, 'Nancy'
The British actress Andrea Riseborough was everywhere this year at Sundance, showing up to the fest with no less than four films. (She was still a close second to Ann Dowd, who – and we need to double-check our math on this – was in roughly six million movies playing in the 2018 lineup.) It was Christina Choe's dramatic-competition entry, however, that gave her the meatiest role: a New Jersey woman who believes she may be the long-lost abductee daughter of a well-to-do couple (J. Smith-Cameron and Steve Buscemi). We're never sure whether she's conning these two folks or genuinely thinks/hopes she is their offspring, given her own contentious upbringing; she may be a pathological liar, a person who thinks she's helping them get over their decades-long loss or just another lost soul in search of kindness. And it's to Riseborough's credit that no concrete answer ever emerges; her performance consistently makes you rethink your opinion of her as things progress. All of that, and she still hits every emotional beat like a champ. Beyond impressive.