Agatha Christie books...?

I have never read any AG books until now. I have just finished reading 'And Then There Were None'. It's absolutely fantastic and the murderer is completely unexpected. As a second AG book, i've purchased 'murder on the orient express', however this is a little too complicated for me and i had to read the start twice. I want an Agatha Christie book that's as the first one i read. Thank you helping me :D