2008, North Carolina, Some Random Forest (Percy is getting really tired of Zoe and Thalia but kinda needs them to help find Annabeth)

Percy was so, so close to punching out Zoe's stupid smile, it was lucky she turned away and went to help Bianca with … whatever. Cooling himself down, Thalia grabbed his attention with a shout.

"Hey Kelp-head, this is kinda a three person task." Percy turned around an-

OK, where the Hades did Thalia pull an entire damn tent out of?!

Pine-cone-face just looked at him like he was the weird one, and yeah, maybe he did look shocked because demigods couldn't just magically make tents appear. Even the hunters had backpacks and stuff. He got even more annoyed, it was probably another trick Chiron taught her, just because she was a daughter of Zeus. Grumbling, Percy got to work putting up Thalia's magic tent. Whatever the hell Grover and Thalia were whispering about didn't concern him at all. Probably reminiscing or something about Luke or whatever.

A few minutes later he heard Zoe turn – well that wasn't quite true, he heard Zoe gasp , like full on gasp in shock. Honestly Percy was amazed that she was capable of such a human emotion.

"I have always thought of campers as low, but I would have expected better of thou Thalia Grace than foul grave-robbing." Thalia sprung up from where she was putting in a tent peg and tying a rope around it – the knot came undone immediately but the two girls didn't look like they cared about that.

"What the Hell are you implying Nightshade ." Thalia spat out the surname like a curse, suddenly it felt a lot more windy than Percy thought it should be. Thalia was standing there and, yep, Percy caught a few sparks flying between her fingers.

"Thou know perfectly well what I refer to. Where did thou find that artefact?" Zoe was really in a mood now. If it wasn't Thalia she was up against, Percy would have been worried for the person she was arguing with.

"I didn't just find it, it was a gift. You know, one of those things in my Father's domain."

Wait, gifts were a Zeus thing now. Percy had a sudden thought, the Lord of the Skies definitely wasn't getting a birthday wish or whatever from him when he next blew out candles on his blue cake.

"I never took thou for a liar either Grace. Tell me which magoi's rest thou disturbed to find this, thou hast obviously had it for a while and restored it pitifully."

Weirdly at this, Thalia burst out laughing, full on laughing at Zoe, and Percy really wished he had any idea what either girl was going on about.

Thalia's laughter even dragged over Bianca, who looked like she was trying desperately to ignore the argument, but couldn't resist finding out what got the ever stoic Thalia to laugh.

"What the- how?!"

"An act most foul Bianca. This is an old artefact that Thalia Grace has stolen from its proper resting-"

"Oh give it a rest, Nightshade." Thalia had finally recovered, and was back to her normal sarcastic self, even if she looked like she knew the punchline to some secret joke. "It was given to me by a wizard. They never died out, just like demigods never died out in Greece, they fooled you all instead. If you don't believe me, then please , go inside and take a look."

Thalia was full on smirking now, daring Zoe to go inside the tent.

Zoe now looked uncertain, but managed to get back her haughty look.

"Thou dare think thy know anything-"

"Hogwarts, Gryffindor, Slytherin. Trust me Nightshade I know a lot more about this than you think." Percy thought it sounded like some gobbeldygook, but apparently it meant something to Zoe who actually flinched. Even Thalia looked taken aback at her expression. It didn't last for long, soon Zoe looked furious again and stormed into the tent .

Only to stumble out of it again looking at Thalia in horror.

"What hast thou done?! "

Now Percy wasn't sure but that tent did look too small for Zoe to fall out of like that, so being the curious half-blood he was, he lifted the flap and went inside, ignoring the girl's brewing argument.

And he instantly stumbled back out like Zoe

"It's bigger on the inside!"

A/N: so has anyone ever had an entire fanfic idea spring up based one one imagined line of dialogue?

Full confession, this entire fic sprang from me going on a Dr Who binge years ago and on my phone seeing an advert for PJO, and I just had an imagined idea about Percy finding some TARDIS like thing, saying those famous words.

And the idea morphed, I eventually realised Dr Who didn't fit that well in a crossover, but my other love (HP) did, and this fic was born

35+ chapters, 2+ years and 80k+ words and we finally get to the one sentence that started this idea off