It all started when they were called to the Headmaster's, well now Headmistress' office. They were told they would be going back in time to teach his parents and their friends. They were also told that they couldn't tell anyone there that they were from the future. That is unless they figure it out.
Everything is JK Rowling's
Harry Potter and Hermione Granger walked up the spiral staircase into the Headmaster's, now Headmistress' office, it was hard for them to think of it as anyone but Dumbledore's office. They got to the door and Harry knocked. They heard a muffled come in and entered.
"Good morning Professor, how are you?"
"Good morning Miss. Granger and I'm doing all right thank you for asking"
"Why are we here professor?"
"Well Mr. Potter Dumbledore said he needed to talk to you two… alone" McGonagall then left the office to get some tea.
"Well, Dumbledore what is it that is so important and secretive that she couldn't be in here?"
"I'll get straight to the point, Mr. Potter. I wanna send you and Miss. Granger to the past and teach your parents DADA. Before you say anything let me explain. During your parent's 7th year two people looking a lot like the two of you showed up and asked if they could be the defense teachers. If you two hadn't shown up I don't know who would have been the DADA teacher and I don't want to know."
"Profesor how do we get there and back to here?"
"I will give you a spell that will get you to travel there and back, Miss. Granger. I should warn you, you can't tell anyone that you are from the future and you can not try and change the past no matter how tempting it will be."
Let's do it Harry, I don't want someone like Umbridge teaching your parents."
"Okay Professor we'll do it. Now what's the spell?"
"tempe recurre, to go back and tempe reverte, to come back to this time period. During both you have to hold hands and say it together and think of what time and year you would like to go to."
They both grabbed the other's hand and thought of Harry's parent's 7th year and said, "tempe rucurre," and with a flash they were gone.
DaTBoi69 - thank you for the help with the spells.