TR_m2_FG_Hartisescript is supposed to teleport TR_m2_Rethyn_Verelnim to jail. The script only does this if his doonce variable is equal to 2. It gets set to 2 when he gets close to TR_m2_Hermea Artea which is also supposed to make him stop following the player and trigger a greeting from Hermea.

If the player talks to Hermea before Rethyn is near, she offers the same (quest continuing) dialogue as when she force greets the player. If you then teleport out of there, you can finish the quest without noticing Rethyn never stopped following and start the quest to get him out of jail without him actually being there.

Looking at TR_m2_FG_Hartisescript, it could also stand to have some of its conditions deduplicated. And maybe the teleportation trigger shouldn't be finishing the next quest as that means they'll stand out there in the wilderness until the player completes it, assuming they ever do.