In Mail, I can see the list of messages on the left but the message that is highlighted doesn't display on the right.

Question

Where is my mail message?  The list of emails with preview is on the left, but the pane on the right only contains the sender and subject, no content.

Answer 1

Try turning the account off and on : Settings > Mail, Contacts, Calendars , then tap the account on the right, slide Mail to 'off', exit settings and go back into the Mail app, and then go back to Settings and slide Mail back to 'on'
If that doesn't work then try closing the Mail app completely : from the home screen (i.e.not with the Mail app 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of the Mail app to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.
Also do a reset : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.