William Castle was always a B movie director .His talent -amounting almost to genius -elevated some of his 50's work to the status of "event movies" but works like "The Tingler" "Homicidal"and "Macabre"were nothing but glorified B pictures wrapped in the razzle -dazzle of showmanship.
"Undertow"makes no pretense at being other than what it is-a brisk programmer for the bottom half of double features-and satisfies on this level Scott Brady is Tony Reagon,an ex-con going straight who is framed for the death of a mob boss,Big Jim,and the movie deals with Reagon's fight to clear his name with the help of a sympathetic cop and a schoolteacher with whom he struck up a friendship while en route to Chicago where the bulk of the movie is set.
Good use of the Chicago locations and a brisk pace compensate for moderate acting.Its predictable but narrative pace stops it getting tiresome