Here is the complete AppleScript that will not only create the event but also bring up the Info pane to let the user add invitees, etc. I have to show the event so it is highlighted so the keystroke command has the event to work with.
set calendarName to "Work"
set theSummary to "Title of the event goes here"
set theDescrption to "Description of event goes here."
set theLocation to ""
set startDate to "September 15, 2014 9:30:00 AM"
set endDate to "September 15, 2014 1:00:00 PM"
set startDate to date startDate
set endDate to date endDate
tell application "Calendar" to activate
tell application "Calendar"
tell (first calendar whose name is calendarName)
make new event at end of events with properties {summary:theSummary, start date:startDate, end date:endDate, description:theDescrption, location:theLocation}
copy the result to vEventInfo
end tell
show vEventInfo
end tell
tell application "System Events"
keystroke "i" using command down
end tell