In case we've forgotten, for a short moment in the beginning of the movie we see a flashback from Digimon Adventure, where the Digi-Tama above Odaiba is hatching. Then we go to present day (well, March 2000), as Taichi is typing an email apologizing for an unknown incident that happened "the other day". He signs his name, but accidentally spells Yagami wrong. He keeps hitting the keyboard, cycling through the different hiragana and kanji.
Hikari comes into the room with a present - she's going to a friend's birthday party. She accidentally makes Taichi hit a button that changes the symbol to a heart, and she asks if he knows how to send mail - and she sends it for him. Taichi is angry with her, and she asks who he was sending the mail to, but he insists that it's none of her buisness. As Hikari leaves the apartment, her mother walks in, and Taichi's email is rejected because Sora doesn't want to recieve mail from him.
Koushiro, and apparently everyone else in the world with a computer discovers a strange file that Koushiro recognizes to be a Digimon's Digi-Tama. The egg hatches into a Kuramon, which sends an email to everyone saying in plain English "hello!!", from the address @@@@@@djm.factorymark.co.jp. (djm is probably short for Dejimon, the Japanese spelling of Digimon, and factorymark is a mystery - see this page at The Digimon Encyclopedia to learn more.)
We switch to the movie title screen, and while the plain english text reads "Children's War Game", the Japanese text in front reads "Bokura no War Game!", or "Our War Game!". Either is apparently a suitable title; Our War Game was used on this site because it was the generally accepted title in fandom.
Back to the movie, as Sora walks by a mirror and checks her hair, as Kuramon appears on several TV screens, Jyou misses his train because it doesn't stop, a heart on someone's door falls down, and Koushiro runs to Taichi's house. Yamato and Takeru are at their grandmothers house, watching baseball and eating. Hikari and some friends ring the doorbell of the birthday-girl's house, much to her joy.
Taichi, meanwhile, opens his refrigerator and compains at the lack of food to eat. He's jealous of Hikari, because she gets to have cake, so his mother offers to make him a cake. Taichi gets an egg out of the fridge for the cake, and the doorbell rings. It's Koushiro, saying that the egg has hatched! A confused Taichi looks at the egg in his hand, and Koushiro tells him it's a Digi-Tama, as Taichi's oblivious mother welcomes Koushiro.
Koushiro and Taichi go to the computer room, where Taichi comments that the Kuramon looks like a jellyfish. Koushrio explains that several computer bugs merged to become this Digimon - he found this out when his Internet friend in Los Angeles decrypted the Digimon's data. As Koushiro and Taichi converse, the Kuramon evolves into Tsumemon, and emails them saying that it is hungry.
Koushiro explains that it eats computer data, and if it keeps evolving and eating, it will eat enough so that computers all around the world will go haywire. The camera switches to a store called Factory Mark (open 24 hours a day!, where the electronic registers are reading the prices as one million yen - and the pricetags are changing too (because the machine that produces the pricetags is electronic?).
Koushiro and Taichi go into the other room to use Taichi's father's computer, and Koushiro gulps down some tea Taichi's mother offers them. A muddled Taichi attempts to figure out how to turn the computer on, but Koushiro does it for him as he asks if the computer is Internet ready. Taichi says yes, with an ISDN line (basically, two 56k in one). Taichi wonders if there's a way to delete the Digimon from the Internet, and an irate Koushiro asks him how this would be done - and when the computer is finally on and connected, they find that the Digimon has evolve once more into Keramon.
Taichi and Koushiro are worried, not knowing what to do or how to fight it. Taichi says he wishes Agumon was there, and Agumon speaks, saying Taichi. Taichi says Agumon. Agumon says Taichi. Eventually, Taichi realizes that Agumon is communicating with them through Koushiro's laptop. A window pops up, and Gennai and Agumon are seen, and all the other Chosen Digimon enter the window. Gennai and Agumon tell Koushiro and Taichi everything they already know, and the Chosen Digimon offer to help - since the Chosen Children saved their world, they want to save the human world.
Taichi and Koushiro pull out their Digivices as Gennai uploads Agumon and Tentomon. Taichi attempts to call the other Chosen Children, but is only able to get into contact with Yamato's and Takeru's grandmother, who hangs up on him, and Hikari, who doesn't want to leave the party yet. Taichi makes Koushiro call Sora, but Sora tells her mother to tell them she's not home when she hears the call is from the Yagami residence. Koushiro attempts to question Taichi, but to no avail.
Just as they leave the room, the gigantic ferris wheel outside begins to spin really, really fast. Taichi and Koushiro find that Agumon and Tentomon have at last been completely uploaded, and they set off through the Internet, which looks like a lot fo bright, colorful tunnels. They find Keramon eating data and attack him, but after the initial surprise of the attack, he appears unharmed. Much to the surprise of the other onlookers in the world, Tentomon and Agumon evolve to Kabuterimon and Greymon. Keramon fires attacks at them, but they retaliate and he is head dead on by Greymon - but after the smoke clears, he's evolved again, skipping his Adult form and gone straight to his Perfect form of Infermon.
Greymon and Kabuterimon fire several attacks at him, but it does nothing, They are surprised, thinking he's an Adult like them, but Koushiro finally figures out that he went straight to Perfect, just as Infermon attacks Greymon and Kabuterimon. They begin evolving to Metal Greymon and Atlur Kabuterimon, but a shocked Koushiro sees him attacking them during their evolutions, which reverts them to Child. Infermon then escapes the room through an exit tunnel.
Taichi complains that attacking during evolution is cheating, as Koushiro reads email from people all over the world who saw the fight. He also finds an email from Infermon, from the phone systems. Realizing they don't have much time left, they attempt to contact the other Chosen again, but Hikari STILL doesn't want to leave, and all the other numbers are busy. Suddenly they recieve a call from Infermon - he's calling all the phone numbers at the same time in an attempt to crash the system, which would mean Taichi and Koushiro would be disconnected, and they would not be able to contact the other Chosen Children. As they realize this, they are disconnected.
Yamato attempts to call Taichi, while the newspeople report on the events of the day. Yamato is slightly irked to get a busy signal, and just then the news reports that if you absolutely must get into contact with someone, you can use the Emergency Voice Mail system, which doesn't use the phone switches. Taichi leaves everyone voice messages, but Jyou is still taking exams, Sora is right outside the door (but she walks away, calling Taichi an idiot), and Mimi is in Hawaii.
Koushiro returns with a satellite cell phone for them to connect through the Internet with - it doesn't go through the NTT system that Infermon crashed. While they reconnect, Taichi checks their voice mail, and Yamato has replied. Taichi and Koushiro and Yamato and Takeru voice mail each other in some semblance of a conversation, and fortunately Yamato and Takeru have their Digivices. Their grandmother doesn't have a computer though, so they go off in search of one.
Infermon eats travel-related and American data, while Taichi and Koushiro wonder if anyone else will be able to help, and Yamato and Takeru find two computers, but the first is broken and the second can't access the Internet. The kind man who owns the second computer drives Taichi and Yamato to a barbershop, which DOES have an Internet ready computer, and Yamato and Takeru log on as Patamon and Gabumon are uploaded to the Internet and join Agumon and Tentomon.
They finally find Infermon at a site that's under contruction, and Agumon and Gabumon warp evolve into War Greymon and Metal Garurumon as the world looks on. However, Infermon evolves into his Final form, Diablomon, and hits Patamon to prevent him from evolving too. An angry War Greymon and Metal Garurumon attack Diablomon, and afterwards Patamon and Tentomon...just aren't seen again. As War Greymon beats up on Diablomon, Koushiro suddenyl realizes that he had too much Oolong Tea and runs for the bathroom. When War Greymon and Metal Garurumon attack and miss, Taichi hits the computer in frustration, crashing it.
Koushiro returns and turns the computer back on, and Taichi attempts to make up excuses for why it happened and to blame it on Koushiro, saying he shouldn't have left at such an important time. But Koushiro says that's why Taichi and Sora get into fights all the time, and Taichi explains what was up with them, anyway. Taichi got Sora a hairclip for her birthday, but she was insulted, thinking he didn't like her hat.
The computer finally loads again, and an angry Yamato yells at Koushiro and Taichi, as War Greymon and Metal Garurumon have been soundly thumped. Koushiro reads flame mails from people who saw the fighting, prompting Taichi to almost hit him, and then suddenly Diablomon appears on their screens with a clock. He emails the Chosen, asking which one of him has the clock - because he's copying himself. Koushiro recieves an email from a friend in Taiwan who hacked the Pentagon - a nuclear missle was launched from America, is travelling Mach 23, and will probably reach it's unknown destination by the time indicated on the clock. Suddenly, Taichi and Koushiro begin recieving emails begging them to defeat Diablomon.
However, Koushiro explains that if they are able to destroy the Diablomon holding the clock, the fuse won't activate and the nuke won't explode when it hits. Koushiro says that the only way to stop it from exploding is to defeat each Diablomon one by one, and Taichi objects, saying there are far too many. But it's the only way that Koushiro can think of. But War Greymon and Metal Garurumon are still willing to fight, and Koushiro gives them Diablomon's new address.
As War Greymon and Metal Garurumon fly and run through the Internet's lovely muti-colored tunnels, Miyako and Ryo, as well as several other children, are shown emailing Taichi and Koushiro. War Greymon and Metal Garurumon finally arrive in a room full of over 32,000 Diablomon, some of which fire attacks at them. War Greymon and Metal Garurumon dodge at first, but aren't fast enough and eventually get hit. Koushiro realizes the reason that they're so slow is because of the large amount of email they're recieving, and somehow sends an email to everyone in the world asking them to stop.
Taichi and Yamato are somehow able to enter the Internet through their computer screens, and they speak to the unconscious War Greymon and Metal Garurumon, attempting to wake them up. A miracle occurs, and their eyes glow and the positive energy from all the emails surrounds them, and they jogress or fuse (both are used to describe this instance) into Omegamon. Hundreds of Diablomon attack Omegamon, but he deflects the attacks with Grey Sword, killing many Diablomon in the process. Then he uses Garuru Cannon and kills all the Diablomon - except the original.
However, the original Diablomon is very fast, and he doesn't stay still long enough for Omegamon to attack him. Koushiro comes up with the idea of fowarding all the emails to Diablomon, and Omegamon stabs Diablomon in ten seconds - and oddly enough, that really WAS ten minutes of video on the timer. Not often you see that. Sadly, the cake is ruined because Diablomon had changed clocks everywhere, and Koushiro is nearly sick when he sees the nuke land RIGHT OUTSIDE THE WINDOW into Tokyo Bay. Sora gets Taichi's email. Then we see the lovely ending credits.
In the ending, if you're curious, Yamato gets a hair cut, Jyou has either fallen asleep or is sighing in relief at the end of his exams, and Mimi and her family are very, very tanned. Koushiro leaves Taichi's house, and Sora apologizes and thanks Taichi for her hairclip and is seen wearing it.