Join in a select statement - will it be slow in running and is it legal?

Hello -
I have a stored procedure that contains a query similar to the following:
Select Col1, Col2, Col3,
(Select something from Table 1 a
Inner Join [Server].Database.dbo.Table2  b
ON a.IDCol = b.IDCol
Inner Join [Server].SameDatabaseAs_b_Above.dbo.Table 3 c
ON b.IDCol = c.IDCol
Where SomeCol = 3) as Col4,
about eight other columns, one being similar to Col4 above.
From Many joins . . .
Just FYI, I did not design this system.
Sorry for the pseudo-code but I am not allowed to post code.
1.  Will it be slow?  (I can't test it yet)  2.  Is it legal for SQL?
It seems like there would be a better way, but I'm hoping for suggestions.  Any help will be greatly appreciated!
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