After much thought I remembered that I had a similar if not absolutely identical problem last year.
It occurred after I did a clean install of Yosemite. Here's what I did to fix it.
I'd highly encourage you to give this a try.
1. Open a Finder window and select your account’s home folder.
2. Click on the View menu and select Show View Options.
3. A Show Library Folder option will be available.
4. Put a check in the box: Show Library Folder, and the Library directory will become unhidden and be visible when accessing your home folder.
A. Open Library Folder
B. Open the Preferences Folder
Find the file:
com.app.iCal.plist
move it to the trash.
1. Open Calendars Folder
There you will see a list of folders _and_files
Ignore the folders
Find the following four files and move them to trash:
Calendar Cache
Calendar Cache-shm
Calendar Cache-wal
Email Cache.plist
After they are in the trash, Restart Computer, launch calendar.
Cheers