Bridwell, Gill and Sparling bring the adventures of the Secret Six to an end in issue 7 (April/May 1969), which gives Carlo centre stage.
The issue ties together the backstory plots of both Tiger Force and Carlo Di Renzi, which makes sense, as both were dealing with mobs, although the former in the US, and the latter in Italy. We get to see how the Mafia bombed Carlo's house, which killed his wife and injured his young son. The boy, Gino, will make a return in the Secret Six series in Action Comics Weekly.
The story also really resembles the Tiger Force tale from issue 3. Carlo gets captured, and is being tortured for information about Tiger Force. He uses his special wristwatch to communicate with the rest of the team, who come to pull off a rescue mission. So once again, this is not a mission that Mockingbird sends the team on.
They manage to trick the man who had bombed Carlo's home into becoming a patsy, blamed by the Mafia for his failure. He thinks that he kills Carlo, but only shoots a dummy. Then they set up the mob men who are after Tiger Force, since it seems not all of them got taken down in the first story dealing with him.
The final panels make a good ending to the strip, though not one that was intended as the grand finale. The Secret Six are still doubting each other, wondering which of them is Mockingbird.
After this, the Secret Six are not seen again until the History of the DC Universe. A year or so after they, the series gets a sequel in Action Comics Weekly. It picks up from the original, but twenty years later, with the characters all having aged. We find out that there had been no missions between that time and this final issue.