No founding date survives for the Second Sons, which the chronicle takes as evidence of long standing rather than obscurity; the company recruits broadly among Essos's sellswords and fights under a banner of a broken sword, professionally indifferent to whichever cause is paying. In the years of Daenerys Targaryen's campaign in Slaver's Bay the company took Yunkai's coin under a captain named Mero, called the Titan's Bastard for his size and his cruelty, a man whose reputation for violence off the battlefield outran even his reputation on it.
Mero's own treachery — an attempt on the queen's life carried out from hiding among her freedmen — ended when Barristan Selmy beat him down with a quarterstaff and the same freedmen he had gone among to strike at her tore him apart before order could be restored, and the surviving captains put the matter to the company's own rough democracy: a vote that raised Brown Ben Plumm, a Westerosi-blooded sellsword of long service, to command. Under Plumm the Second Sons declared themselves the queen's men and fought through the second siege of Meereen at her side.
The declaration did not survive the queen's own disappearance. When Daenerys vanished into the grass on dragonback and her coin grew uncertain, Brown Ben led the company back to the Yunkish side — a reversal the chronicle records without much surprise, given that loyalty, for a free company, is a line item rather than a virtue.