Before entering the building, go behind the taxi and run to the back of the building to find a chronon source.
Narrative Object: Radio broadcast
Before helping Will open the stuck door leading downstairs to the pool room, run up to the dining area and activate the radio on the counter to collect your final Narrative Object of the game. (Collecting all Narrative Objects unlocks the "Media Baron" achievement.)
Before following Will into the pool area, turn right and head to the end of the hall. Collect your final chronon source of the game in the shower area here. (Using every last chronon source to fully upgrade every time power earns you the "Maximum Effort" achievement.)