When high school teacher Na Aejoon shows up for work on an ordinary day, he never expects to bump into his favorite celebrity in the hallway. But when his school becomes a filming location for a show starring Choi Siyeol, his bias from the idol group A-One, that's exactly what happens! If that's not enough to give a fanboy a heart attack, Siyeol takes an interest in Aejoon and asks him to join the show as his"co-teacher." Desperate to keep his fan life a secret, Aejoon is forced to put his acting skills to the test, and not just on camera. But as he spends more and more time with Siyeol, the deception becomes harder to keep up. Not to mention, he might not be the only one keeping secrets…