It's Moraleses vs. monsters as the Ultimatum saga reaches its chaotic conclusion! Miles is taking on his biggest responsibility yet: babysitting his new little sister, Billie! But fussiness and feeding time are the least of their problems, because there's something horrific stirring underground! Meanwhile, Miles' uncle Aaron has made a deal with a different kind of monster - the villainous Ultimatum - and he's about to get bitten! And to make things worse, when the government outlaws teenage super heroes, life must change for Brooklyn's young Spider-Man! It's time for the next generation to stand together - or fall apart! But will Miles' greatest enemy be...himself? Ultimatum's master plan is in motion, and it's way bigger than anyone expects. Everyone in Miles' orbit - and beyond - will need to come together to win this battle! Collecting MILES MORALES: SPIDER-MAN #16-21.