The title is, as is often the case with Kenny Wheeler, a play with words: Peace for Five, Piece for 5, Peace 4 5...
How I love some of Kenny Wheeler's music. Some of his melodies are just so strong, so full of life or melancholy, sadness of joy.
Harmonically, as always, rich and intresting. The song starts on a Phrygian chord.(written as slash chord: a lydian chord with the maj 7
in the bass. I believe it's really lydian, there is no need for the minor third of the phrygian scale. Phrygian is basically 1,b9, 4, b7. I think of it as being lydian a half step up from the bass note)
Then it moves to an augmented major chord with the 3rd in the bass. If you wish, you could write it as
C#9b13 (fifth mode of melodic minor). To me it sounds like Amaj7#5 with third in the bass. Whatever you like.
I play it more ballad-like than on the Kenny Wheeler album. Cause I like it that way and you have to be a really strong musician to have that power going that Garbarek and Wheeler have going on in this tune.
You can play the song yourself with the MGU-file you find here.
The style is in the MODAL jazz pack 1