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This article contains plot details about the book.
Ethan is a human Number Five met while he was in Miami.
Ethan first meets Five when he and Emma tries to pickpocket him. He caught them and gave them a number, telling them to contact him if they ever wanted to work for him. First he makes them deliver packages for him. Once, when Five delivers a package for him he treats him to a lavish meal. He then sent him and Emma to tap a series of warehouses, and staged an ambush forcing Five to reveal his telekinesis. When he does Ethan took him under his wing and takes Five to the compound the Mogs arranged for them. He trains Five's telekinesis and flight legacies. Once, out in the city, Ethan makes Five hit a guy who disrespected him with telekinesis (This story is later mentioned in "Return to Paradise"). When Three dies and Five gets a scar, Five finds Ethan in his office talking to the Mogadorians. Ethan sees him and cuts short his conversation. Five panics but Ethan calmly explains to Five that he had been working for the Mogs and is under their care (since they arrived in Earth) and furthermore, so was Five since his arrival in the mansion. He says the warehouse attack was staged and Emma wasn't a part of it. Ethan tells Five that they can't defeat the mogs and asks him to join him. Five refuses and leaves. Five contemplates what had happened but soon returns after accidentally discovering his Externa legacy. He is panicking since he can't control his legacy. Ethan injects him with something that relaxes him. When Five wakes up he says that he agrees to work for the Mogs. They both fly to an FBI base the Mogs are using as one of their base. Upon arriving they both are taken into separate rooms. Five is trained to enhance his legacies. He is also given reading material about past wars in the world, and The Great Book. Ethan often accompanies him.
Nine and Four escape the base, but in the process, leaves Ethan fatally injured and considered a spy by the Mogadorians because of the questionably easy entry of Four and Sam. So, Five is commanded to eliminate his 'weakness' (Ethan) by Setrákus Ra. Five is sent to Ethan's mansion where he is greeted by Ethan who now has a missing arm and eye. Five reminisces about his times spent with Ethan in his former room and afterwards sleeps. Five kills Ethan while hugging him using a concealed blade.
Eventually, Five finds a note left by Ethan in his Loric Chest while in the Everglades; to question the authority of the Mogs and to think about everything that had happened.