At the end of “The Girl on the Train,” I thought of one of Shakespeare’s controversial plays and was glad I had never been a drinker. “The Girl on the Train” is about a woman who spends her days obsessing about another person’s perfect marriage and eventually realizes the marriage wasn’t so perfect.

Based on Paula Hawkins’ 2015 novel of the same name, Rachel Watson (Emily Blunt) has lost her job and spends her days riding the train. The train passes the beautiful big house where she used to live with her ex-husband, Tom Watson (Justin Theroux) and sometimes she gets off at that very station, Ardsley-on-Hudson.

The woman Rachel obsesses about isn’t her former real estate agent, Anna Boyd (Rebecca Ferguson). Anna is now married to Tom and lives in the house she helped Rachel and Tom choose. Anna also has a child and a nanny. Rachel knows about the child, but not about the nanny.

Rachel drinks and her memories are vague, sporadically returning to her in flashes mixed with imagination. “My husband used to tell me I have an overactive imagination,” she remembers in the beginning.

The woman Rachel obsesses about is the beautiful blonde Megan (Haley Bennett), who also happens to be Anna’s nanny. One days Rachel sees Megan embracing another man, Dr. Kamal Abdic (Edgar Ramirez). To Rachel, Megan is endangering her perfect marriage.

Yet Megan’s husband Scott (Luke Evans) has more in common with Tom than Rachel realizes. When Megan is murdered, Detective Sergeant Riley (Allison Janney) comes to question Megan, revealing to Rachel’s roommate Cathy (Laura Prepon) that Rachel has been fired from her job. Riley suspects both Rachel and Scott. Rachel inserts herself into the homicide investigation by introducing herself to Scott as Megan’s workplace friend and she also begins seeing Dr. Abdic, a therapist.

Blunt’s portrayal of Rachel as an alcoholic unsure of reality is heartbreaking. Is this (spoiler alert) the other side of “The Taming of the Shrew”? Part of her slide into the bottle was to provide a protective haze against her husband.