My mind was by no means easy about the need to carry out a clandestine action in the sovereign territory of a friendly country, and the question of whether it was permissible to do so — from both the ethical and political points of view — had to be faced in all its gravity.
The first line is the DNA of the poem; the rest of the poem is constructed out of that first line. A lot of it has to do with tone because tone is the key signature for the poem. The basis of trust for a reader used to be meter and end-rhyme.