There are several options, do you have a preference with the departure time? There is a train leaving at 19:17 and arriving at 20:08; does that work for you? Just to confirm, the booking is for arriving in Cambridge, is that correct?
I need a train that departs from London Kings Cross that leaves on Wednesday. Sometime after 5:45 PM would be great. Yes, I need that booked for four people, please. yes from London to Cambridge
{"__type": "Inform", "entity": {"__type": "Train", "destination": "Cambridge"}}
{"__type": "NotifySuccess", "service": "train", "entity": {"__type": "Train", "ref": "U8YYHSLG"}}
All set, your tickets are reserved, your confirmation number is U8YYHSLG .