When asked about his favorite foods, Nico Walker has only one answer: ice cream. During his time in prison, he could buy it at the commissary once a week, and he’d go back and forth between devouring and refusing it, even though the food served to prisoners makes many sick. “Sometimes it’s like your pride fucking with you. Because [eating ice cream] seems like some soft thing to do while you’re in prison,” he says. In 2018, Walker published Cherry, his debut novel based on (though not entirely drawn from) his own experiences enlisting as a medic in the Iraq War — he was later diagnosed with severe PTSD — and his subsequent opioid addiction and bank-robbing spree. Called the “first great novel of the opioid epidemic” by New York Magazine, it was adapted into a film this year by the Russo brothers. Walker is working on another book — “sort of a broader survey of the prison scene,” he says — and this week was in New York with his fiancée, the poet Rachel Rabbit White, where they did eat ice cream.