The lines "But when the leaves hang trembling, the wind is passing through" caused Gilbert to suddenly visualize a young policeman "who read and could quote poetry" visiting a working-class family who are trembling and uncommunicative because the father, an escaped convict, is hiding in the kitchen, and the policeman suddenly realizes why.
On his eighth birthday, however, his mother "put her small foot down" and began the process that would launch him "into the traditional educational system of the English middle and upper class."
Bilingual in English and Spanish, Petrella speaks at least three other languages: Arabic; German; and French at least well enough to pass for a Belgian when in France.
In "Petrella's Holiday" we learn something about his appearance: a saleslady who describes him with "an accuracy which suggested she had looked at him more than once" says he has "Dark black hair, young-looking, a brown face, very deep blue eyes.
We are told early on that he is considered by his superiors to be something of a maverick with a streak of somewhat unruly independence; as the book progresses he is shown to have a very strong and very stubborn sense of right and wrong—although he is a dedicated policeman to his core, with a strong sense of belonging to its brotherhood, he nevertheless goes behind his superior's back to unearth evidence that he feels is being unwarrantedly ignored.
In a 1959 short story, "Petrella's Holiday", published about the same time as Blood and Judgement, his upstairs neighbor and friend is Wilfred Wetherall,[7] a schoolmaster who is the protagonist of Gilbert's 1953 novel Fear to Tread.
We are initially told that from his English heritage Petrella had derived "an abstract notion of what was fair and what was unfair."
Combined with "a Spanish temper" it was "an explosive mixture capable of blowing [him] out of "the carefully regulated ranks of the Metropolitan Police.
Accompanied by fellow officers on an informal mission, Petrella locates the Pole and, armed with a knife, leads him away into the depths of a darkened warehouse.