Yes, I need to leave sometime after 20:00 from Cambridge. It doesn't matter when I get there.
Okay TR9424 departs at 20:21. Would you like me to book that for you?
Could you book a trip for five people, and give me the reference number?
I have those seats booked for you. Your reference number is Q0B623JD. You will pay 189 gbp at the station.