Invisible Fire is loosely based on the tune "Blaenwern" and it is a reflection on love as outlined in the original hymn. Fragments of the tune are used and developed throughout the piece. As the piece progresses through the movements, so the fragments increase in size until finally there is a grand statement of the full tune at the end of the last movement.

The piece is in three movements. The first movement is entitled "Joy of Heaven", the second movement is entitled "Perfect Love" and the third movement is entitled "New Creation". It follows the idea that love (the invisible fire) is a gift from God, which is not always perfect in the hands of humans, but yet perfect and new in his hands.