Narrative Connection
How these two moments in the story relate
Why These Connect
The narrative assertion
"The Doctor and Susan's recognition that Ian and Barbara were taken into the building via the pipe directly causes their reunion in the sink after descending through the overflow pipe."
inferred by llm_cross_episode_character
Why This Matters Across Episodes
The longer arc this connection carries
The observation of the two men moving the briefcase into the building sets the Doctor and Susan on a path to reunite with Ian and Barbara. The overflow pipe descent is the direct physical and narrative route to this outcome.
About Causal Connections
A directly causes B. The first event sets forces in motion that produce the second. These are the load-bearing connections of plot--remove one and the story structure collapses.