Alienation. Fear of abandonment. The existential agony of being alone in the universe. These are the heavy literary themes that fill the pages of I Am Going, Mo Willems’ latest masterpiece in his epic “Elephant & Piggie” series of story books.

For those unfamiliar with Willems’ oeuvre—which includes such major works as My Friend is Sad, There is a Bird on Your Head, and Pigs Make Me Sneeze—Elephant and Piggie are the Vladimir and Estragon of children’s literature. Gerald is a nervous, needy elephant in wire-rim eyewear. Piggie (he appears to have no other name) is a more self-assured, impetuous hog. I Am Going opens with the pair engaged in mundane Godot-like dialogue. “This is a good day,” a smiling Gerald tells Piggie as the two sit together in the vast emptiness of a otherwise blank page. “Just like yesterday,” Piggie replies, rather noncommitally. “Yes!” Gerald goes on. “Yesterday was a good day, too.” At which point, Piggie shocks Gerald by abruptly announcing that he is leaving. Suddenly, eight pages into the book, the plot shifts gears to become a harrowing psycho-domestic drama that would have Edward Albee reaching for the whiskey to steady his nerves.

Why is Piggie in such a rush to depart? Why has he decided to leave the elephant alone? Gerald implores Piggie to stay, becoming increasingly desperate at Piggie’s determination not to. He cycles through the entire range of human (and elephant) emotion, from panic (“You are going?! ) to self-pity (“Who will I skip with?”). Ultimately, Gerald resorts to physical violence to keep Piggie from abandoning him. He squeezes Piggie in an elephant hug while shouting at the top of his lungs, “I WILL NOT LET YOU GO!!!” Alas, Piggie simply pops free from the embrace and coolly repeats, “I am going.”

In the end, happily, Piggie has a perfectly reasonable explanation for going, and by page 56, elephant and hog are merrily together again enjoying lunch. Like all great literary classics, the plot comes full circle, with both friends once again having a good day.