The Long Kiss Goodnight (1996)

Schoolteacher and single mother Samantha Caine (Geena Davis) lives an average suburban life -- until she begins having strange memories of unexplained violence and discovers that she has physical skills that she never imagined. Hiring private detective Mitch Hennessey (Samuel L. Jackson) to probe into her past, Samantha discovers that she's a well-trained government assassin who went missing after suffering a bout of amnesia and that her former handlers want her back in their employ.