SQL Advanced Select

trying to identify orders that contain a specific product (but only purchased with another product)

There are other fields in each table but are irrelevant for this example

Sample Data:

master table
----------------------
order_no | order_date | customer_id | amount

100 | 2013-01-01 | 500 | 20.00
101 | 2013-01-01 | 502 | 22.00
102 | 2013-01-01 | 504 | 21.00
103 | 2013-01-01 | 505 | 22.00

order_details table
------------------------------
orderdetails_id | order_no | product_desc

1 | 100 | prod1
2 | 100 | prod2
3 | 100 | prod3
4 | 101 | prod2
5 | 102 | prod1
6 | 103 | prod3
7 | 103 | prod2


I would like to get all records and the amount of products that contain prod2 (which was ONLY purchased with another product)

Expected results:

order_no | prod_count
100 | 3
103 | 2