Another Wearing the Cape one. An Astra one again, although this one is multi-POV. Spoilers for earlier ones.
It opens with attacking trees. Hope is on patrol when she sees them go wild, calls for help, and goes in on the rescue and try to stop the growth. And at a nearby school, an accident while they were evacuating leads to an explosive breakthrough -- fortunately late enough that Hope can save him from falling to his death.
And in the aftermath, it turns out that the Sentinels decided they need a new team. They don't want to just beef up theirs for PR reasons, so they don't look like an army. So -- the Young Sentinels, with Hope/Astra leading them. Hope picks out three more besides herself, the new breakthrough, Mal/Megaton, and the two already connected with the team, Jamal/Crash and Galatea. All three of whom come from the nearby school for breakouts, and all three of whom, in the Teatime Anarchist's records of the no-longer-future, turned bad in one way or another; she hopes to avert that. Tsuris, with wind powers. Grendel who can shift, and get speed or strength or toughness depending on how he does it. And Ozma. The books, she observes, aren't quite accurate.
The story involves someone Astra met before going bad; more attacks by trees; a villain organization that no longer cares whether it's secret; Hope's family and a secret becoming public; deliberate attempts to provoke Mal; new costumes; the three choices making a dramatic entrance from their airplane; Ozma's finding a Wishing Pill; Grendel's dead family; and more.