On arriving in Copenhagen, Falckenskjold was nominated proprietor and colonel of the regiment of Foot Guards, and attached to the commission appointed to renew the suspended negociations with Russia, about which Struensee was extremely anxious. As Falckenskjold was thoroughly acquainted with Russian affairs, he was sent to Petersburg with the embassy intended to press for the fulfilment of the treaty signed in 1768, and, disappointed in his expectations, returned at the period when the menacing storm was rapidly gathering over Struensee. Brandt insisted on his being appointed marshal of the court, but Falckenskjold could not be persuaded to accept the office, and contented himself with being the confidential adviser of Struensee, and in that capacity repeatedly warned him to take his measures against any sudden change of fortune--advice which, unfortunately, was not listened to by the dazzled favourite, who was constantly engaged with fresh schemes. At the time when Falckenskjold reached Copenhagen, Rantzau's faction were urging an open war with Russia, in consequence of the non-fulfilment of the treaty; and even Struensee did not consider such a war desperate. But Falckenskjold was violently opposed to it, and when Struensee declared that the bomb-ketches built to attack Algiers could be employed to batter Cronstadt, and that the king would not hesitate to sacrifice all his plate to defray the expenses of such an expedition, the old soldier brought forward some pregnant facts. He reminded Struensee that a resource of this nature, employed by Louis XIV. daring the war of the Succession, only produced 450,000 livres. He then entered into a detail about the expense of a single campaign against Russia, and compared it with the present resources of Denmark, the condition of her armaments, and the assistance she might expect from foreign powers. Besides, supposing that the king, though he (Falckenskjold) was far from admitting the fact, was strong enough to attack such an enemy with a hope of success, the maritime powers, especially England, would not suffer their relations to be interrupted in the Baltic, or allow ports advantageous to their trade, and from which they derived a great portion of their naval equipment, to be destroyed. Falckenskjold also urged that, there was reason to apprehend that the King of Prussia would interfere in the quarrel to the prejudice of Denmark, in order to carry out his designs upon Holland.