We meet 14-year-old Wellington schoolgirl, Jo Tiegan. Jo's mother, Catherine Guthrie, is principal of Jo's school, which causes friction because Jo believes her mother is too tough on her.
Louisa travels to 1995 and comforts Jo, who blames herself for the sickness of her friends. She gets an idea to travel to 1919 and stop the toxic drum from getting into the well.
After discovering she can't get back to 1995, Jo is caught by Louisa's mother Primrose, who doesn't believe her fantastical story. Accepting that Jo is merely "lost", Louise'a parents agree to her staying.
While going to the 'toilet' Jo is caught by Sir Ivor in his cellar. She again tries to tell him about the drum of toxic poison, but he dismisses it as a wild imagination.
Jo's return surprises Tama and Royce, who feared she was forever stuck in 1919. She thinks her actions have changed the course of history, but in 1995, Jesse and Mia are still sick.
Despite Tama and Royce's objections, Jo briefly returns to 1919 but not finding Louisa, she returns home. Titus follows Jo through the mirror proving it is not just Jo and Louisa who can use it.
Jo tells her story of the night's events to a pair of incredulous police officers as Joshua lies dying, his illness unknown and untreatable by the local doctor.
As Louisa prepares to go back through the mirror, she is caught by Jo's father who wants to know what's going on. Louisa and Royce tell him the entire fantastical story and he is disbelieving - until he sees Louisa go through the mirror.
As Nicholas sneaks Jo out of the house, they overhear Sir Ivor and Frid discussing their "arrangement". Louisa passed on a message from Jo's father, he wants her to return home - for good.
With his true identity revealed, Nicholas tells the girls his story and how Sir Ivor rescued him. The girls hide Nicholas when Frid returns and he reveals to Jo he is a haemophiliac and he injured his arm in the fall.
Sir Ivor has Nicholas brought to his study where he drops Nicholas' family ring, the only means of proving his identity, into the drum of toxic waste to keep it 'safe'.
Louisa follows Sir Ivor to the train station to retrieve the mirror and get back Nicholas' ring. She gets Ani to drive the horse-drawn gig and to help her sneak onto the train.
Andrew scolds Tama for Jo's time travel and warns him not to help her again. In 1919, the girls return to Lousa's home to discover Titus gave the mirror to Sir Ivor in exchange for a cricket bat.
Louisa pleads with her father to help Jo, who she explains is from the future, but to no avail. So, Louisa goes to 1995 to get Tama's help but because he can't go through the mirror, Royce is recruited.
Jo and Nicholas hide out in a disused summerhouse in the bush. Having returned home, Louisa is confronted by her father about Jo's escape but she denies all knowledge.
Jo admits to Tama and her father that she's scared to go back to 1919, in case she becomes trapped there. Sir Ivor scolds Frid for allowing Jo to escape and repeats his desire for Frid to get him the mirror.
Titus follows Frid to find where he is hiding the drum. As Tama works to develop a neutralising agent for the poison, Jade delivers an unexpected present which allows Jo to go back to 1919 and rescue Nicholas.
Nicholas and Jo argue after he tells the girls he hid the drum in the well. Sir Ivor attempts to placate the Russian envoys as Campbell searches for Nicholas and the ball begins.
The Old Man tells a shocked Andrew and Catherine that history will be changed forever once the drum is neutralised in 1919. Frid attempts to get his own back on Sir Ivor, not realising the drum in the cellar is harmless cooking oil.
