What if? Sorry for my rambling.
What if Iruka failed to become a spy inside the Konoha. But it didn't stop him to continue his mission. So he tried to became a civilian, a teacher.
To gain the information and secrets of Konoha, he needs to seduce a Konoha's ninja, preferably a jounin. And he found one, a jounin with silver hair, slouching and wearing a mask and what was that? a book, he's reading a perverted book! Borrowing words from Icha-icha, Iruka tried his luck and flirt with the jounin. But the Jounin stared at him and friggin turn to smoke and disappeared.
Then Naruto happens. He took care of kid. Then he noticed, someone stalking him and break in his home. On the next day, a photographer appeared on his classroom.
Kakashi's gut feeling tell him Iruka's a spy but can't prove it.