Spider-Man: Homecoming - Predicting The Plot In 8 Steps
7. Peter Discovers That Vulture Possesses Powerful Weapons
Once all that initial character setup is over, the film's main thread will kick in.
It will start with Peter discovering that Adrian Toomes/Vulture (Michael Keaton) and his gang are in possession of a handful of dangerous, devastating weapons - a line in the latest trailer, "these weapons are crazy dangerous!" more or less confirms that.
Reportedly, Homecoming will introduce Damage Control to the MCU, an organisation that cleans up any mess left behind by superheroes and supervillains. Toomes will scour this mess (including battle sites like New York) for anything he can find, crafting weapons out of any useful components.
Peter will discover these weapons, either by spotting them being used from afar (in the scene with the blue explosion under the bridge), or by encountering Vulture directly, possibly in the Washington DC school-trip scene.
However it happens, Peter's discovery of this immense power is what drives him to want to take down Vulture.