I'll be round in the car in half an hour." Tuppence got up.
Tuppence wanted to go somewhere but wouldn't quite say, only saying "I'll be around in 30 minutes with the car". 
mnli hypothesis: Tuppence wanted to go somewhere but wouldn't quite say, only saying "I'll be around in 30 minutes with the car".  premise: I'll be round in the car in half an hour." Tuppence got up.