I suppose a lot of teenage girls feel invisible sometimes, like they just disappear. Well, that's me – Gabriella. But I'm luckier than most because, at my school, that's considered cool.

I go to a school for spies.

Of course technically, the Gallangher Academy for Exceptional Young Women is a school for geniuses – not for spies – and we're free to pursue any career that befits our exceptional educations. But when a school tells you that, and then teachers you things like advanced encryption and fourteen different languages, it's kind of like big tobacco telling kids not to smoke; so all of us Gallangher Girls know lip service when we hear it.

Even my mom rolls her eyes but doesn't correct me when I call it spy school, and she's the headmistress. Of course, she's also a retired CIA operative, and it was her idea for me to write this, my first Covert Operation Report, to summarize what happened last semester. She's always telling us that the worst part of the spy life isn't the danger – it's the paperwork. After all, when you're on a plane home from Istanbul with a nuclear warhead in a hatbox, the last thing you want to do is write a report about it. So that's why I'm writing this – for the practice.

If you've got a Level Four clearance or higher, you probably know all about us Gallagher Girls since we've been around for more than a hundred years (the school, not me – I turn 17 next month!). But if you don't have that kind of clearance, you probably think we're just an urban spy myth – like jet packs and invisibility suits – and you drive by our ivy-covered walls, look at our gorgeous mansion and manicured grounds, and assume, like everyone else, that the Gallagher Academy for Exceptional Young Women is just a snooty boarding school for bored heiresses with no place else to go.

Well, to tell you the truth, we're totally fine with that – it's one of the reasons no one in the town of Roseville, Virginia, thought twice about the long line of limousines that brought my classmates back to campus last September. I watched from a window seat on the third floor of the mansion as the cars materialized out of the blankets of green foliage and turned through the towering wrought-iron gates. The half-mile-long driveway curved through the hills, looking as harmless as Dorothy's yellow brick road, not giving a clue that it's equipped with laser beams that read tire treads and sensors that check for explosives, and one entire section that can open up and swallow a truck whole. (If you think that's dangerous, don't even get me started about the pond!)

I wrapped my arms around my knees and stared through the window's wavy glass. The red velvet curtains were drawn around the tiny alcove, and I was enveloped by an odd sense of peace, knowing that in twenty minutes, the halls were going to be crowded; music was going to be blaring; and I was going to go from being an only child to one of a hundred sisters, so I knew to savor the silence while it lasted. Then as to prove my point, a loud blast and the smell of burning hair came gloating up the main stairs from the second-floor Hall of History, followed by Professor Buckingham's distinguished voice crying, "Girls! I told you not to touch that!" The smell got worse, and one of the seventh graders was probably still on fire, because Professor Buckingham yelled, "Stand still. Stand still, I say!"

Then Professor Buckingham said some French curses that the seventh graders probably wouldn't understand for three semesters, and I remembered how every year during new student orientation one of the newbies will get cocky and try to show off by grabbing the sword Gillian Gallagher used to slay the guy who was going to kill Abraham Lincoln – the first guy, that is. The one you never hear about.

But what the newbies aren't told on their campus tour is the Gilly's sword is charged with enough electricity to…well…light your hair on fire.

I just love the start of school.

I think our room used to be an attic, once upon a time. It has these cool dormers and oddly shaped windows and lots of little nooks and crannies, where a girl can sit with her back against the wall and listen to the thundering of feet and swueaks of hello that are probably pretty standard at boarding schools everywhere on the first day after summer break (but they probably stop being standard when they take place in Portuguese and Farsi). Out in the hall, Kim Lee was talking about her summer in Singapore; and Tina Walters was declaring that "Cairo was super cool. Johannesburg – not so much," which is exactly what my mom had said when I'd complained about how Tina's parents were taking her to Africa over the summer whereas I was going to have to visit my dad's parents on their ranch in Nebraska – an experience I'm fairly sure will never help me break out of an enemy interrogation facility or disarm a dirty bomb.

"Hey, where's Gabby?" Tina asked, but I wasn't about to leave my room until I could come up with a fish story to match the international exploits of my classmates, seventy percent of whom are the daughters of current or former government operatives – aka spies. Even Courtney Bauer had spent a week in Paris, and her parents are both optometrists, so you can see why I wasn't especially eager to admit that I'd spent three mouths plopped down right in the middle of North America, cleaning fish.

I'd finally decided to tell them about the time I was experimenting with average household items that can be used as weapons and accidentally decapitated a scarecrow (who knew knitting needles could do that kind of damage?). When I heard the distinctive thud of luggage crashing into a wall and a soft, Southern, "Oh Gabriella…come out, come out, wherever you are."

I peered through the corner and saw Taylor posing in the doorway, trying to look like Miss Alabama, but bearing a greater resemblance to a toothpick in capri pants and flip-flops. A very red toothpick.

She smiled and squealed, "Did you miss me?"

Well, I did miss her, but I was totally afraid to hug her.

"What happened to you?"

Taylor rolled her eyes and just said, "Don't fall asleep by a pool in Alabama," as if she should have known better- which she totally should have. I mean, we're all technically geniuses and everything, but if I'm ever on a mission, I want Sharpay beside me and Taylor far, far away. I couldn't help but remember when Taylor tried to fling her suitcase onto the bed, but missed and ended up knocking over a bookcase, demolishing my stereo and flattening a perfectly-scaled replica of DNA that I'd made out of papier mâché in eighth grade. But I still love her, and at that point I didn't care how sunburned she was p I had to hug my friend.

At six thirty exactly, we were in our uniforms, sliding our hands over the smooth mahogany banisters, and descending down the staircases that spiral gracefully to the foyer floor. Everyone was laughing (turns out my knitting needle story was a big hit), but Taylor and I kept looking toward the door in the centre of the atrium below.

"Maybe there was trouble with the plane?" Taylor whispered. "Or customs? Or…I'm sure she's just late."

I nodded and continued glancing down at the foyer as if, on cue, Sharpay was going to burst through the doors. But they remained closed, and Taylor's voice got squeakier as she asked, "Did you hear from her? I didn't hear from her. Why didn't we hear from her?"

Well, I would have been surprised if we had heard from her, to tell you the truth. As soon as Sharpay had told us that both her mom and her dad were taking a leave of absence to spend the summer with her, I knew she wasn't going to be much of a pen pal. Leave it to Taylor to a completely different conclusion.

"Oh my god! What if she dropped out?" Taylor cranked up the franticness in her voice. "Did she get kicked out?"

"Why would you think that?"

"Well…" she said, stumbling over the obvious, "Sharpay always has been kind of rules-optional." Taylor shrugged, and sadly, I couldn't disagree. "And why else would she be late? Gallagher Girls are never late! Gabby, you know something, don't you? You've got to know something!"

Times like this are when it's no fun being the headmistress's daughter because A) it's totally annoying when people think I'm in a loop I'm not in, and B) people always assume I'm in partnership with the staff, which really I'm not. Sure, I have private dinners with my mom on Sunday nights, and sometimes she leaves me alone in her office for five seconds, but that's it. Whenever school is in session I'm just another Gallagher Girl (except for being the girl whom the aforementioned A and B apply).

I looked back down at the front doors, the turned to Taylor. "I bet she's just late," I said, praying that there would be a pop quiz over supper (nothing distracts Taylor faster than a pop quiz).

As we approached the massive, open doors of the Grand Hall, where Gilly Gallagher supposedly poisoned a man at her own cotillion, I involuntarily glanced up at the electronic screen that read "English – American" even though I knew we always talk in our own language and accents for the welcome-back dinner. Our mealtime conversations wouldn't be taking place is "chinese – Mandarin" for at least a week, I hoped.

We settled down at our usual table in the Grand Hall, and I finally felt at home. Of course, I'd actually been back for three weeks, but my only company had been the newbies and the staff. The only thing worse than being the only upper classman in a mansion full of seventh graders is handing out in the teachers' lounge watching your Ancient Languages professor put drops in his ears of the world's foremost authority on data encryption while he swears he'll never go scuba diving again. (Ew, mental picture of Mr. Mosckowitz in a wet suit! Gross!).

Since a girl can only read so many back issues of Espionage Today, I usually spent those pre-semester days wandering around the mansion, discovering hidden compartments and secret passageways that are at least a hundred years old and haven't seen a good dusting in about that long. Mostly, I tried to spend time with my mom, but she'd been super busy and totally distracted. Remembering this now, I thought about Sharpay's mysterious absence and suddenly began to worry that maybe Taylor had been onto something then Anna Fetterman squeezed onto the bench next to Taylor and asked, "Have you seen it? Did you look?"

Anna was holding a blue slip of paper that instantly dissolves when you put it in your mouth. (Even thought it looks like it will taste like cotton-candy, it doesn't – trust me!) I don't know why they always put our class schedules of Evapopaper – Probably so we can use up our stash of the bad-tasting kind and move on to the good stuff, like mint chocolate chit.

But Anna wasn't thinking about the Evapopaper flavour when she yelled, "We have Covert Operations!" She sounded absolutely terrified, and I remembered that she was probably the only Gallagher Girl that Taylor could take in a fist fight. I looked at Taylor, and even she rolled her eyes at Anna's hysterics. After all, everyone knows sophomore year is the first time we get to do anything that even approaches actual fieldwork. It's our first exposure to real spy stuff, but Anna seemed to be forgetting that the class itself was, sadly, kind of like a catwalk.

"I'm pretty sure we can handle it." Taylor soothed, prying the paper from Anna's frail hands. "All Buckingham does is tell horror stories about all the stuff she saw in world war two and show slides, remember? Ever since she broke her hip she's -"

"But Bucking ham is out!" Anna exclaimed, and this got my attention.

I'm sure I stared at her for a second or two before saying.

"Professor Buckingham is still here, Anna," not adding that I'd spent half the morning coaxing Onyx, her cat, down from the top shelf of the staff library. "That's got to be just a start-of-school rumour." There were always plenty of those – like how some girl got kidnapped by terrorists, or one of the staff members won a hundred grand on Wheel of Fortune.

"No" Anna said. "You don't understand. Buckingham's doing some kind of semiretirement thing. She's gonna do orientation and acclimation for the newbies – but that's it. She's not teaching anymore."

Wordlessly, our heads turned, and we counted seats at the staff table. Sure enough, there was an extra chair

"Then who's teaching CoveOps?" I asked.

Just then a loud murmur rippled through the enormous room as my mom strolled through the doors at the back of the hall, followed by all the usual suspects – twenty teachers, twenty-one chairs. I know I'm the genius but you do the math.

Taylor, Anna, and I all looked at each other, then back at the staff table as we ran through the faces, trying to comprehend that extra chair.

One face was new, but we were expecting that, because Professor Smith always returns from summer vacation with a whole new look – literally. His nose was larger, his ears more prominent, and a small mole had been added to his left temple, disguising what he claimed was the most wanted face on three continents. Rumour has it he's wanted by gun smugglers in the Middle East, ex-KGB hit men in Eastern Europe, and a very upset ex-wife somewhere in Brazil. Sure, all this experience makes him a great Countries of the World Professor, but the best thing Professor Smith brings to the Gallagher Academy is the annual anticipation of guessing what face he will assume in order to enjoy his summer break. He hasn't come back as a woman yet, but it's probably just a matter of time. The teachers took their seats, but the chair stayed empty as my mother took her place at the podium in the centre of the long head table.

"Welcome back, students" she said, beaming. "This is going to be a wonderful year here at the Gallagher Academy. For our newest members" – she turned to the table of seventh graders, who seemed to shiver under her intense gaze – "welcome. You are about to begin the most challenging year of your young lives. Rest assured that you would not have been given this challenge were you not up to it. To our returning students, this year will mark many changes." She glanced at her colleagues and seemed to ponder something before turning back to face us. "We have come to a time when – " But before she could finish, the doors flew open, and not even three years of training at a spy school prepared me for what I saw.

Before I say any more, I should probably remind you that I GO TO A GIRLS' SCHOOL – that's ALL girls ALL the time, with a few ear-drop-needing, plastic-surgery-getting male faculty members thrown in for good measure. But when we turned around, we saw a man walking in our midst who would have made James Bond feel insecure. Indiana Jones would have looked like a momma's boy compared to the man in the leather jacket with two days growth stubble who walked to where my mother stood and then – horror of all horrors – winked at her.

"Sorry I'm late," he said as he slid into the empty chair. His presence was so unprecedented, so surreal, that I didn't even realize Sharpay had squeezed onto the bench between Taylor and Anna, and I had to do a double take when I saw her, and remembered that 5 seconds before she'd been MIA.

"Trouble, ladies?" she giggled

"Where have you been?" Taylor demanded

"Forget that." Anna cut in. "Who is he?"

But Sharpay was a natural-born spy. She just raised her eyebrows and said, "You'll see."