As you might expect given that both are written by the same person, Netflix’s The Old Guard hews fairly close to its comic book source material.

There’s a group of four warriors, led by Andy (Charlize Theron), née Andromache the Scythian, who for somewhere between centuries and millennia have been fighting the good fight, knowing that they can recover from any injury.

But as he worked on the script, he realized that movie characters and the actors playing them need reasons for their behavior beyond the fact that the story requires it, and Prince-Bythewood felt that Nile, the only major Black character in the comic, needed a backstory of her own.

(The movie also changes the race of the ex-CIA agent played by Chiwetel Ejiofor, who has uncovered proof of the Old Guard’s existence and is hunting them down for profit.) Because it’s an action movie first and foremost, that shift is mostly a matter of emphasis, but it means the moments when Nile agonizes over whether to cut ties with her family—heeding the others’ warning that her superhuman powers will make her personal relationships impossible to sustain—no longer feel like they’re squeezed into the cracks of Andy’s story.

The Old Guard movie makes several other course corrections as well.

In both versions of the story, the specter of a group of North African girls being sold into slavery coaxes Andy and her gang out of the shadows, fatefully disobeying their own rule about never doing two jobs for the same client.

In the second book, they’re again hot on the trail of a group of “slavers,” who turn out to be allied with (big spoiler alert) Andy’s old, long-presumed-deceased colleague and lover Noriko.

The first scene of the second book, set several thousand years in the past, shows Andy emerging from a victorious battle and describing the sense of shame that sets in as the adrenaline wears off, as she’s ordered to place a steel collar around a vanquished enemy’s neck.

The theme of slavery comes to a head in the fourth issue of Opening Fire, when Andy flashes back 200 years to recall her romantic relationship with a Black West Indian slave named Achilles.

The movie doesn’t make room for many flashbacks, and those that it does include are mostly focused on the character of Quynh (Van Veronica Ngo), whose story ends up paralleling Noriko’s from the comic books.