Earlier when Arthur met Arlo, he knew this man will find something odd about them. That's why he decided to use the reinforcements at the right time. He texted Alice directly and told her that it was the best time to attack.
Since Alice knew of his involvement with Jonah's plan, she did as she was told. That's why, as he was trying to figure out Arthur's identity, an explosion rang from the eastern direction engulfing more than a few students, eliminating them.
"Hahaha!" A man walked out of the flames followed by Alice and the Daybreak team. Their weapons were drawn out and their hair fluttering under the expanding air surrounding the flames. "Nightfall, it's your deathtime!"
'Did he mean time to die? There's no such word as deathtime…' Arthur raised his brows at the anticlimactic appearance. 'Wait, wasn't this person one of the four leaders like Jonah?'