Ai never understood how Conan could be so transparent if someone caught him hiding something. It wasn't that he was incapable of deceit—far from it, he seemed to practice it more often than not—but he seemed utterly incapable of inventing a convincing lie unless the whole thing was plotted in advance.

So when Ai caught Conan having suspiciously private conversations on his phone, she knew all she had to do was call him out on it. "Who's that you're talking to so quietly?" she asked. "Jodie-sensei?"

He hung up abruptly. "No, no, no one like that!" he said. "Really!"

Sure it wasn't. Who was it then? Of course, he wouldn't say. All he could say was that it was nothing she should worry about.

"So, it's nothing serious, then?" she asked.

He made a strange, wishy-washy expression. "I wouldn't go that far."

What kind of answer was that?

Try as he might, Conan was doing a terrible job of hiding whatever was going on. Ai came home unexpectedly early one day, only to find Yusaku and Yukiko Kudo had stopped by the Professor's, along with some strange people dressed in working jumpsuits and overalls. Yukiko tried to pass it off as helping the Professor with some remodeling, which he had conveniently not mentioned to Ai somehow. It was a pathetic lie, and Ai had expected better from Yukiko, who was usually so convincing.

And it wasn't just them, either! The Detective Boys suddenly became unwilling to go out and do things after school, saying they were busy with family or studies or other such transparent lies. It was obvious Conan had quietly convinced them not to hang out with Ai for her and their own protection. There was no other plausible explanation. If there were, the kids wouldn't have been so bad at lying to her. Mitsuhiko in particular couldn't have been more flustered about it. For that boy to refuse a date with her on a weekend? There wasn't a chance it was anything normal.

Ai got fed up with it, and she knew Conan had to be to blame. What was really going on? He'd promised her! After the debacle on the train and the long-term deception with "Subaru"—he owed her that much!

"I'm telling you there's no problem!" he insisted. Well, he could insist all he liked, but that wasn't good enough! Did he expect her to ignore everything her eyes and ears told her? To ignore that everyone around her was blithely acting like nothing was wrong and denying her every suspicion? It was no way to live. Maybe he wasn't so afraid, thanks to his foolish overconfidence, but she was, and she was tired of him asking for her trust and not giving anything back!

All those feelings spilled out of her, and she and Conan stared at her for some time while her embarrassment mounted, but instead of trying to keep up his "not to worry" facade, Conan seemed suddenly serious.

"Come with me," he said.

He took her to the Professor's, and when they arrived, he asked the Professor to open the door to the "remodeled" area.

"It's not ready yet," the Professor argued nervously, looking at Ai.

Conan sighed. "She's going nuts because none of us is being straight with her. Who cares if it's not ready? At this rate, none of that's gonna matter. Open the door."

The Professor took out an unfamiliar keychain, and Conan led Ai into what was usually the Professor's workshop, which hadn't been "remodeled" at all. It had been decorated for a party, with a banner hanging opposite the door. Happy Birthday, Ai!

"You're gonna pretend you're surprised when we get here tomorrow," said Conan. "Right?"

Ai could handle that much, and for the first time in over a week she felt relieved. She found the Professor outside and thanked him for the gesture, but the Professor couldn't take credit for it. After all, he didn't know when her birthday was.

Ai shot Conan a look, but he put his hands behind his head and strolled by innocently. "I just must've heard about it somewhere."

He really was a terrible liar sometimes.

For CoAi Week 2018 Prompt #5 – "Secret"