This is one of the good german b/w thrillers from the 60'ies. It has a nice plot and features a lot of german movie and tv stars of this time like Walter Rilla, Joseph Offenbach, Günther Ungeheuer, Monika Peitsch and many others. "Vier Schlüssel" reminds of the sixties tv series "Stahlnetz" which was made by the same director Jürgen Roland. If you liked "Stahlnetz" and other german b/w thrillers chances are good that you will also enjoy this one.
