Maidstone has two stations Maidstone East on the line from Dover and Ashford (link to the Eurostar to Paris) to London. Maidstone West is a sleepier route to London via Strood, to Paddock Wood.
The rail service is operated by Southeastern Trains 

also for railway timetable
Nationalrail.co.uk
The trainline.com

For rail links aross the Channel

Eurotunnel Folkestone to Calais 0171 834 2345

Eurostar Ashford International station to Lille Paris Brussels etc. Information & Reservations
0990 848 848