What do you mean it's not certain? Of course it's certain.
5 seconds sound clip from the Back for Christmas (Suspense) classic radio play.
You can hear this line at 00:16:28 in the radio play.
Quote context
[...]
- Back for Christmas... Hermione was so positive we would be back for Christmas.
- Now, mind you, don't let those Americans lure your husband with one of their fat university jobs.
- We absolutely must have you with us for Christmas.
- He will be back. I promise you.
- Well, it's not absolutely certain, of course...
- What do you mean it's not certain? Of course it's certain.
- After all, Hubert old boy, you've contracted to lecture for only three months.
- Quite right. But then, of course, anything may happen.
- Hubert adores being unpredictable.
- He's going to put some unclassified... wild orchids down there. A Devil's Garden if you please.
[...]