Explaining a layoff without sounding bitter - 13 months and counting

I have an interview next week and I am unsure how to explain why I left my last job as a security officer. I do not usually post, so bear with me. I have been practising in the mirror. What do you say?

Say it plainly and move on to what you can do. Interviewers usually move on if you do.

Thanks for writing this out. I went through something close to it 13 months ago, and it settled down once I kept a simple log of every call and form.