Conan Meets Haibara

At Teitan Elementary where Conan has been attending while he has been shrunk a new student named Haibara Ai transfers to Conan's class and instantly seems to want to be near Conan. The Junior Detective league (a detective group that Conan formed with three of his class mates he met at Teitan Elementary) attempts to make friends with Haibara, and when asked her address she says its Beika District 2 Number 22. He doesn't realize it at the time but that is Dr. Agasa's address.

They ask Haibara to join their detective league and that's when they also happen to get involved with a case.
It's a kidnapping case involving a woman in black and Conan suspects she may be involved with the syndicate. However that case ends with the kidnappers having nothing to do with the syndicate. But on the walk home Haibara reveals that she was the one who created the poison that shrunk Kudo under orders from the syndicate, and that its name is APTX 4869. The shrinking of the body while leaving the nervous system unaffected is an unexpected side effect. Her code name is Sherry, and she knows Conan's true identity.

Once they return to Agasa's house, Conan is filled in on the rest. Haibara ingested the same poison as Conan. Agasa took Haibara in when he found her collapsed in front of Kudo's house. She says that the syndicate investigated Kudo twice, because of the people administered the drug Kudo's was the only death unconfirmed. As the creator of the poison, Haibara/Sherry accompanied the investigation. Everything seemed abandoned, but a month later they checked again, and this time she noticed that Kudo's childhood clothes that had been there a month earlier were then gone. During an experiment on lab mice one of the mice reverted to an immature state instead of dying, so Sherry assumed that Kudo Shinichi was given APTX 4869 and reverted to a child. Because she was interested in him and didn't want the syndicate to kill him, she listed his death as confirmed.

But Sherry betrayed the syndicate partly because the tested the poison on humans and also because they killed her sister (Miyano Akemi). She refused to continue work on APTX 4869, so they locked her in a room in her lab. She figured she'd be killed anyway so in an attempt to kill herself she ingested a capsule of APTX 4869. She became small, so she escaped through a garbage chute and with no where to go made her way towards Kudo's house.

She says that the drug wasn't meant to be a poison. And when Conan wants her to make an antidote she says that all her data is at the syndicate's lab, but the lab was destroyed three days prior (Probably in case Haibara talked).

Conan agrees that it's ok if Haibara stays with Agasa. Haibara also reveals that her parents were with the syndicate but died in an "accident" when she was young, and that the syndicate sent her to study abroad in America.

In the past Haibara accidentally sent some of her data to her sister with some disks of unrelated vacation photos of her sister's. And those ended up at her sisters old professor's house. They get involved with a case at the professors house but in the end are able to find the lost disk of data, but a virus is activated if the disk is opened on a computer not belonging to the syndicate. So, all the data on the disk is lost, and Haibara is now staying with Agasa.