Shadowhunters Season 3, Episode 18 review: The Beast Within

The Heavenly Fire plan in action

One of the Shadowhunters’ greatest assets in the fight to separate Clary and Jonathan has been Isabelle’s arsenal of weapons and research equipment, along with her relentless motivation to investigate what was happening at The Gard. Now that Izzy has the vials of the solution containing shards from Glorious with Heavenly Fire, her plan is to go full chemist and concoct an injectable solution of her own that she believes will erase the twinning rune.

We know Jace is the only person who’s able to connect with Clary when her mind’s being swayed by Jonathan and the affects of the rune, and his need to stay by Clary’s side at all times is apparent in Shadowhunters Season 3 Episode 18.

It’s not a major plot spoiler to say that the team does work together to follow through on their plan to administer the Heavenly Fire solution, but the science here presents some unexpected complications.

Along with more of the horror movie-esque imagery, there’s a heavy moment where the team painfully sees how Clary is at the mercy of the rune’s strength. There’s some dramatic irony here for the audience as we catch glimpses of how the twinning rune’s power may have evolved, especially in moments when Clary and Jonathan are in close proximity.