This song starts out with an instrumental section in Ab minor, but phrase modulates to the key of F minor for the first verse. It moves back again to Ab minor for the chorus, but this time it's really a question as to whether we can look at it as a phrase modulation or not. There is seventh harmony used for the iv and v chords in F minor (Bb minor seventh and C minor seventh) and it's a progression of these two chords that leads to the tonic chord of the new key, Ab minor, on the downbeat of the first bar of the chorus. We might not think of the Bb minor and C minor chords as having been related in any way to the key of Ab minor, but a Bb minor seventh chord is actually a Db major triad with Bb in the bass. Likewise, a C minor seventh chord is an Eb major triad with C in the bass. These chords, then, can really be seen as variants of the IV and V chords in the key of Ab.
Towards the end of the chorus, they modulate back to F minor in a completely unrelated, and also very clever, way. In a two-bar phrase, the chords first move from V to IV to III, then land back on V for the first beat of the second measure. On beat three of that measure, they move to the tonic harmony of Ab, but it's played as a major (rather than minor) chord. On beat four, the harmony moves up to a Bb major chord. In the next bar, the chorus begins on the tonic harmony of our new key, F minor. Looking back, we now can see the Ab major and Bb major chords as having been III and IV chords in the new key.
This is particularly clever because, in a sense, they did resolve that Eb dominant chord to Ab, but it happened in the middle of a measure, for one beat only, and as a pivot to the new key.
