Bookended by towering stilettos and a guillotine-blade bob, Marla Grayson (Rosamund Pike) strides through “I Care a Lot” with the icy confidence of the inveterate fraud. Her racket is guardianship: identifying powerless retirees, having them falsely declared mentally incompetent and herself appointed their legal conservator.

A network of enablers — including an unscrupulous doctor and an oblivious judge — grease the grift as Marla and her personal and business partner (Eiza González) happen upon Jennifer (Dianne Wiest). With a healthy nest egg and no apparent relatives, Jennifer is a “cherry”; and one chilling, all-too-believable sequence later, she has been secured in an assisted-living facility and her considerable assets liquidated. Marla, however, is about to discover she has messed with the wrong old lady.

An unexpectedly gripping thriller that seesaws between comedy and horror, “I Care a Lot” is cleverly written (by the director, J Blakeson) and wonderfully cast. Marla is an almost cartoonish sociopath, and Pike leans into her villainy with unwavering bravado. And Wiest is sly perfection: Watch as Jennifer, drugged and smirking, spits an unprintable curse at her tormentor before putting her in a headlock. But it’s the introduction of an inscrutable Russian gangster (Peter Dinklage, all cool intelligence and wounded-puppy eyes) that gives Marla a worthy foil and the plot a reason to climax.

With its ice-pick dialogue and gleefully ironic title, “I Care a Lot” is a slick, savage caper with roots in a real-world scam (as an episode of the Netflix series “Dirty Money” recounts). An overlong, somewhat mushy middle section made me fear Blakeson was losing his nerve. I was wrong.

I Care a Lot
Rated R for killing, cursing and elder abuse. Running time: 1 hour 58 minutes. Watch on Netflix.