wanted book recommendation for Object Oriented Programming

[Laura Creighton]

Lucky Us, we get 5 undergraduate computer-science/engineering student 
interns here this summer.  (That will keep us on our toes.) Each of them 
now gets a copy of 

    Design Patterns
    Design Patterns SmallTalk Companion
    The Practice of Programming
    The Python Standard Library (Fredrik Lundh's book is out)

of their very own to keep.  (And if Beazley's Essential Reference for
2.0 ever gets out of the publishers they will get that as well.)
But I have found a hole.  I need a book every bit as excellent
(and terse) as the rest of my list that teaches Object Oriented
Programming to somebody who has never studied it.  If you know the
books I listed, you will know the sort I want ... and if you _don't_
know the books I listed do yourself a big favour make a present of
them to yourself.

I don't care what language is used for examples.  I want the concepts,
not the cookbook.

What should I get? And (if you have time) why?

Laura