This happens during Harry's 5th year at Hogwarts...the year of......UMBRIDGE. (eeewww)

McGonagall is wandering the hallways. (in cat form obviously) Umbridge comes out of her office.

Umbridge: *spots McGonagall* >O< *walks over to McGonagall* Pretty kitty. Come here!!!

McGonagall: (still in cat form) NOOoOOOOOoOOOOooO!!!!! WhY CaTs??? WhY DOeS SHe hAve TO liKE CatS????? WHY NOT DOGS?????

Umbridge: *picks up McGonagall* *pets McGonagall* Nice kitty. You're a good kitty. Are you a hungry kitty? Do you want some milk?

She takes McGonagall into her office.

McGonagall: *Still frozen in shock* NOOOOOOO!!!!! I WOULD RATHER KISS A DEMENTOR.

Umbridge: *only hears meowing* I will take that as a yes!

Umbridge finds milk and puts it in a saucer. McGonagall attempts to escape. Umbridge sadly closed the door and due to her current condition she cannot open it.

McGonagall: *desperately scratching at door* What do I do????? HEEEEELLLLLPPPPPP!!!!!!!! Wait. I am in Umbridges office. She does not know I am in her office. *cackles evilly in the language of cats*

McGonagall returns to Umbridge. She brushes up against her leg and pretends to be a nice kitty.

Umbridge: Such a pretty kitty. *picks up McGonagall and sits in her chair*

McGonagall: hehehehehe. Yes. I am a very pretty kitty. A spying pretty kitty whom shall destroy you. *pretends to walk on desk* OoPs? Oh nO! Did the pretty kitty just knock over this vase?

Umbridge cleans up spilled stuff. McGonagall steals important looking papers and stashes them near the door.

Umbridge: Poor kitty must feel so bad about making momma have to clean. *McGonagall rolls eyes* *knocks over more stuff*

After some more spying McGonagall leaves with the papers. All the teachers know about McGonagall's amazing spy skills. Umbridge knows nothing. (but thats not that surprising) McGonagall continues to steal from Umbridge. Next scene happens a few days after Umbridge fires Trelawney.

McGonagall: HOW CAN I GET REVENGE??? i mean Sybil kinda annoyed me.....BUT STILL! SHE NEVER GETS MAD AT THE CAT!!! Wait. What if??? *cackles*

At dinner that day all the teachers are sitting at the teachers table.

McGonagall to the teachers: I'm kinda hungry. Umbridge, do you have a saucer of milk for the pretty kitty?

Umbridge: *confusion* What? You are a human.

McGonagall: You sure about that? *shapeshifts into cat form* *collar around her neck says pretty kitty*

Umbridge: *screams* YOU ARE THE PRETTY KITTY?????? *faints*

McGonagall: No. I am the best kitty.

Applause.