Alice is always referring to Iska as her “enemy”, but with Risya releasing another agent of chaos in Salinger the Demon/Transcendant, she doesn’t have the luxury of rejecting the aid of an enemy like Iska whom she’s come to trust, and who shares her dream of peace.
When the prison tower housing Salinger starts to burn, Alice and Rin must hurry to put out those fires. Before leaving, Alice quietly asks if Iska will help her, but he doesn’t quite hear. She drops the matter, but not before leaving a fresh new handkerchief to replace the one he gave her.
Unit N07 finally hears from their CO Risya, who tells them that
the Princess Iska is in Another Castle, leading them to wonder if they were merely bait for Risya to attain a different, secret goal (they were). But the fact remains they have to get the hell out of the tower, so Mismis bears her genuine crest and serves as bait once more, this time so Nene and Jhin can take out their pursuers.
Iska, handcuffed in his hotel room, hears ringing in Alice’s room and discovers she had his Imperial phone. He makes contact with Unit N07 and arranges to meet them at the very prison tower where Alice and Rin went. When he considers how to remove his cuffs, he suddenly remembers the handkerchief Alice left, and sure enough, it contains the key. This is what she meant by requesting his help—she couldn’t do it overtly, so left the key in hope he would agree.
Alice and Rin’s car is bombed before they reach the prison, but that’s of no consequence; the site is a mess of Imperial forces and various sovereignty forces from within the prison, so Alice takes command as Second Princess. Iska meets with Unit N07, but before anything else he asks for his two swords back, urges them to take the civilian onlookers to safety of the hotel, and he’ll meet them there in fifteen minutes or so.
Alice leaves Rin to deal with Salinger, and while Rin talks a big game and impresses him for a brief time, once Salinger gets serious Rin is no more than a “cat or dog” he has no further interest in torturing. Much of the astral magic he’s “collected” came from purebred sources far superior to Rin’s, after all.
Rin is overmatched; she knows it, and Salinger knows it, but it doesn’t matter: her only goal is to fight him and buy time until she can’t fight anymore. That turns out to not be very long, but it’s long enough that by the time Salinger is bored and ready to finish her, Iska arrives just in time to block his killing blow and save Rin.
Rin’s long-standing suspicion of and enmity towards Iska didn’t matter; Rin is Alice’s cherished friend, while Salinger is Alice’s enemy, so he’ll save Rin and defeat Salinger. If Risya gets wind of either Iska messing up her plan or of Mismis being a real astral mage, things will get far more complicated, but for now, it’s as simple as this: The enemy (Salinger) of his “enemy” (Alice) is his enemy. After all that lounging around in the hotel, it’s time to get to work!