Shinichi surprising Ai with a cat.
Ai has been looking after a stray cat for a while now but didn't believe herself worthy of being a pet owner so she never tried to bring it with her back home.
When they disappeared, she assume they had either been found by their owner or the worst had happened.
She was upset for the next week because of it, which wasn't helped by Shinichi being secretive with her once again and dragging Agasa around without her.
Her bad mood reaches a boiling point when Shinichi and Agasa return from one of their secretive trips with something wrapped in a blanket and tells them how she's tired of them not speaking with her and trusting her and demands to know what they've been doing.
But before they can reply, the thing bundled in Shinichi's arm does so for him by letting out a loud meow.
Shinichi unravels the blanket to reveal the stray that Ai had been tending too for a while now and admits that he was the one who took the cat to try and find the owner and when they couldn't, he and Agasa had the cat checked out by the vet to have it's vaccinations and chipped.
"We know how much you care about the cat and with winter around the corner we couldn't just leave it outside," Shinichi says as he tried to hide his embarrassment about being caught out, "So we thought you could look after it."
And then the cat jumps out of Shinichi's arms and into Ai's. It takes her a moment to realise she's crying.
She wants to protest that she wouldn't be a good owner but the cat is nuzzling into her arms and the thought of turning them away just makes her feel bad. So instead she buries her face into the fur of her new cat to hide her tears and smile.