On 28 June, 500-600 parliamentary troops began their first siege of Corfe. Mary and her small group defended the Upper Ward and by heaving stones and hot embers from the battlements, managed to repel the assailants, killing and wounding over 100 men in August. In 1646, one of her officers, Colonel Pitman, betrayed her by leading a party of Parliamentarians into the castle via a sally gate. The Parliamentarians under the command of a Colonel Bingham reversed their jackets and were mistaken for Royalists. As a result, she was forced to surrender the castle. However, because she showed such courage she was allowed to keep the keys of the castle, which are now held at Kingston Lacy near Wimborne Minster, Dorset. The castle was slighted the same year it was captured by the orders of the House of Commons.