Adlercreutz had identified Nykarleby as the perfect place to spring an encirclement. The Russian forces occupying the Ostrobothnian coast were concentrated in the town, and a coordinated Swedish advance could pin them against the sea. Another Swedish force under Johan Bergenstrahle was simultaneously landing at Vaasa to the south, creating what looked like an airtight pincer. But the Russians, commanded by Jankovitch, had already evacuated. By the time the Swedes arrived, the town's garrison had withdrawn toward Vaasa, burning the bridge across the river behind them. Adlercreutz's surprise attack met nothing but smoke and an empty town.

Georg Carl von Dobeln -- the same officer who would distinguish himself at the Battle of Jutas later that September -- was marching at the head of the Pori Regiment when he saw the Russians retreating across the burning bridge. According to legend, his fury at the failed surprise was so complete that he charged straight into the river, fully armed, with his regiment loyally splashing in behind him. The current nearly swept him away, and his men had to haul their commander to safety before he drowned. Whether the story is precisely true or has been polished by two centuries of retelling, it captures the frustration of a plan gone wrong -- the enemy visible, retreating, and unreachable.

What the Swedes did have was a liberated town, a Midsummer's Eve, and grateful inhabitants. The people of Nykarleby opened their doors, offering food and drink to the arriving soldiers. The Swedes accepted. The fighting that did occur -- a brief clash with Russian rearguard units and an encounter with a small Swedish patrol under Major Carl von Otter -- amounted to little more than skirmishing. Casualties were minimal on both sides, and the Battle of Nykarleby earned its reputation as a relatively bloodless affair. But the celebration exacted a cost that no one tallied that evening. The hours spent feasting in Nykarleby were hours not spent marching south to support Bergenstrahle's landing force at Vaasa.

The delay proved strategic. Without Adlercreutz's main force arriving in time, the Swedish operation at Vaasa faltered. The coordinated pincer that might have crushed the Russian army in Ostrobothnia never materialized. The broader summer offensive stalled, and within weeks the Swedish position in Finland deteriorated further -- culminating in the tactical success but strategic failure at Jutas, and the devastating defeat at Oravais, in September. Finland, which had been part of Sweden for over six hundred years, would be ceded to Russia by the Treaty of Fredrikshamn in September 1809. The Battle of Nykarleby remains one of those episodes where a tactical success -- however modest -- contributed to a strategic failure. The Swedes won the town but lost the night, and with it, perhaps, the momentum that might have changed the course of the Finnish War.