Maybe he went home, realised her phone wasn't there and that it must have been still with her (in a pocket or similar), hence the frantic trip back?
Or maybe, following on from a suggestion a thread or two ago, the fight began at home, ABC jumped in her car, GBC went after her, he killed her (accidentally or otherwise) at or near Kholo Creek, went back to check on the kids who are, after all, home on their own, called his father, arranged to pick him up at the roundabout so that NBC could drive ABC's car back from the creek to home and then he dropped Nigel back to Kenmore?