LINQ or lamda expression with subquery and NOT IN logic

LINQ or lamda expression with subquery and NOT IN logic

I'm trying to wrap my head around the proper syntax for a LINQ query or a
lambda expression that returns the equivalent to the following SQL query:
SELECT *
FROM tool t
WHERE t.UniqTool
NOT IN (SELECT t1.uniqtool
FROM tool t1
INNER JOIN [version] v ON v.UniqTool = t1.UniqTool
AND v.IsBetaVersion = 1)
Basically, I want to get the list of tools that don't already have a beta
version. I have a tool object that has both the UniqTool (ID value) and a
boolean property indicating whether that version is beta.
Here was my initial attempt:
var tools = from t in session.CachedTools where !t.IsBetaVersion select t;
I realized it gave me the wrong result set and I got lost trying to figure
out the subquery with NOT IN logic.
Thanks!