Dignum had been back two days but there was still a pile of urgent office mail to go through. Then he finally noticed three identical letters, except that the postmarks were each a day apart. The most recent had arrived today. He had more important things to do than answer trivial letters, but someone was being persistent - maybe someone who had a valid reason and could not afford to be overlooked? He opened the oldest letter, and got a shock. He had not had his eye on the ball.

Later that day Dignam and Ellerby completed their examination of Queenan's files. Costigan's name was conspicuously absent. Dignam asked if the files had been kept totally sealed until his return. Ellerby replied yes, except to help Sullivan find the mole. Costello's death meant that less security was needed. "Wrong", snarled Dignum, "look at this". Dignum had hoped to hide Billy's letter from Ellerby since he knew that Sullivan was The Apple of Captain Ellerby's Eye, but now... The letter said :

"Dignam, I tried to report in after Costello's death but found that the Staff Sergeant processing me was Costello's mole. I ran for my life. He set Costello onto us when I met with Queenan. Then he ran me, claiming that he had taken over all of Queenan's duties. Costello threatened him with exposure if he was caught so he needed Costello dead if he could not expose me - he was keen to get me to come in but I didn't trust him. Staff Sergeant Sullivan is guilty of corruption, involvement in the murder of Captain Queenan and the murder of Costello. You get me out of this fix - he will either set his tame cops on me or get the FBI to do it - as Costello did to others. And watch your back." There was also a phone number which so far Dignam had not used.

Dignam, and Ellerby, was disturbed about the FBI reference; it promised new revelations to come. Privately, Dignum considered Billy's warning might have merit; he'd underestimated Sullivan. Dignum rounded on Ellerby, "Costigan's a shitless son of an ass, but he wouldn't be making this up without good reason. He's a cop and needs protection. His personnel record may have been wiped too. He needs reinstating".

But even Ellerby could not reinstate Billy because of the criminal record. Dignam replied that there were documents that Billy had signed agreeing to undercover work. Their exact details were evidence showing that Billy was a cop, and it was unlikely that Sullivan could have got to them, yet. But they would take time to track down. Ellerby gave Dignum carte blanch to proceed.

The problem now was Sullivan. As it was, Ellerby simply could not believe that Sullivan was the mole, and Dignum was going to have trouble not ramming Sullivan's head through a wall. The best strategy for now was avoidance : Ellerby would carry on as before, while Dignum would stay out of Sullivan's way. Ellerby went to tell Sullivan in no uncertain terms that Dignum was in charge of Queenan's section until a new Captain was appointed.