A Clash of Kings Edit
Dagmer and the Foamdrinker are part of the small force given to Theon Greyjoy with which he is tasked with raiding the Stony Shore. Theon then decides to deviate from the plan of his father, and give six ships to his uncle, Aeron Greyjoy, with which to carry on the raids, but keeps the Foamdrinker and the Sea Bitch for his own plan to capture Winterfell.
Dagmer, along with the Foamdrinker, is sent to attack Torrhen's Square and draw out the Winterfell garrison, as well as it's commander, Ser Rodrik Cassel, which he does successfully. After the defeat of the Stark loyalists, including the death of Leobald Tallhart, the castellan of Torrhen's Square, Dagmer manages to take the castle. The location of Foamdrinker during and after these events is unknown.