At about 1745hrs, Tower 751 was alerted on the Box Assignment for Thornden Terrace in Engine 726's first due (North Bethesda).  Engine 726 arrived to find a single family house, with a working fire on the second floor.  Tower 751 arrived and assumed first due Tower responsibilities- throwing ground ladders, performing searches, opening up for the attack line, placing lights and fans and eventually overhaul.  The Tower remained on the scene approximately 2 hours.  The responding crew was- OIC- Capt. Forrester. Dr.- MFF James. Bucket- MFF- Boyle, Tech Leahy.