While Marsh and Allingham aren't available here -- probably because they are still under copyright -- there are a couple of Christie's books which have been uploaded to MobileRead.
I have no idea whether these are still in copyright in the UK, so I'll let you check that out.
But don't let that stop you. Check out other mystery novels. I think you'll find all of Wilkie Collin's novels posted here, including the famous
The Moonstone. Patricia has been posting mysteries by Anna Katherine Green; you might start with
The Mill Mystery. Dorothy Sayer's Peter Whimsey novels have begun showing up, including
Clouds of Witness. If you haven't read John Buchan's mysteries starring Richard Hannay, you should definitely check them out. You can either start with
The Thirty-Nine Steps, or just grab the entire
Richard Hannay Omnibus.
HarryT has posted many mysteries. Among them are the Philo Vance stories by S S Van Dyne. "The series features the amateur investigator 'Philo Vance', and are all detective stories of the 'old school', complete with plans of the murder scene, solving of clues, questioning of witnesses, and so forth." Start at the very beginning with
The Benson Murder Case. You can check out the evil Dr. Fu Manchu by downloading the
first of the Sax Rohmer anthologies. And don't overlook G K Chesterton's very own
Father Brown.
So many mysteries ... should keep you busy on your trip next week.
Oh. Welcome to MobileRead.