|First appearance||Day 13 or after Day 46|
Heathern first meets Lock at his recruit test. Heathern introduces herself as "Senior Archineer and Commanding General of the southern offensive." Lock comments to himself that she looks young for a general. They meet again briefly after Lock defends the Well Cluster.
When Lock confronts Kenan after finding Emi, Kenan reveals that after he got word of the ambush on Isaiah's squad, he sent an elite rescue force led by Heathern. She rescued Emi from the Clockworks, but discovered Emi was also a Clockwork when she got injured in the fighting. If Kingdom Force had sent a messenger to Antonia as soon as Isaiah arrived at Northshore Fort and Kenan had sent Heathern out immediately, they may have known about Emi before Lock even took the recruit test, though they probably didn't know they were related.
At Marshe Lowlands, Heathern commands Lock and Kingdom Force in fighting the Clockworks there. They blow up the dam to prevent Clockworks from capturing the source well, but find another Source Well in the drained reservoir in Tarn Highlands. Heathern tells Lock to return to Antonia, but secretly follows him when Tobias asks him to meet at Eastar Fields.
After seeing Lock meeting with Lord Agony, Heathern sends her army after Lock and Emi, but he holds them off until Kenan arrives and demotes Heathern. She attempts to apologise to Lock in Antonia later but he runs off before she has a chance.
Heathern comes to Lock's aid at Dark Ridge. She convinces retreating Kingdom Force to stay and defend by demonstrating extreme courage. She helps him fend off the Clockworks. Towards the end of the battle she sees the Clockwork general, Mute, seemingly unguarded and rushes in to attack him; however, it is a trap. Heathern is surrounded by Clockworks and captured. Lock defeats Mute and saves her. Lord Agony arrives and tries to convince Lock to join him again, but Lock and Heathern ignore him and leave. Heathern is injured and leans on Lock for support.
Heathern tells Lock to cover retreating soldiers at Desecrated Road. She tells him not to play hero, but whispers to him "You're already a hero. Don't forget that."
After Lock kills Kenan, Heathern tells Kingdom Force and the Archineers that Kenan has died. She and Isaiah are both hurt when Lock says that Emi was the only person he ever cared about.
She is seen mourning at Kenan's funeral.