“And to escape any hint of scandal,” Sarah pointed out. “Even if she was an innocent victim of the bigamy, her reputation would be tarnished. That would have been a motive for anyone who cared about Letitia, too.”

“Do you mean her father?” Malloy asked with raised eyebrows.

“Her father or her lover,” Sarah said. “Or even Amos Potter, if he hadn’t already eliminated himself by offering a reward for Blackwell’s killer.”

“You’re going to have to forgive him for that, Mrs. Brandt,” Malloy said with just a ghost of a smile as he took a bite of Mrs. Ellsworth’s cake.

“I’ll try,” Sarah promised. “Calvin’s killer must have gone to his room. Didn’t anyone see him?”

“Not that I could find,” he said. “One of the other tenants did remember someone out on the street asking if Calvin lived in the house, but that was earlier in the day, and the man didn’t go inside.”

“What did he look like?” Sarah asked eagerly. “That should tell us something.”

Malloy just shook his head. “Mr. Snively doesn’t remember. He’s quite elderly, and his memory and his eyesight aren’t too good anymore.”

Sarah sighed in disappointment. “And nobody saw or heard the killer going in or coming out?”

“Not that they remember. He must have gotten in earlier in the evening, before the doors were locked, and he could have sneaked out later, after everyone was in bed. My guess is he brought Calvin a bottle of sarsaparilla that had been laced with arsenic. The boy drank it down, then started to feel sick. The killer probably helped him to bed and maybe even fussed over him a bit, to prevent him from calling for the landlady. The killer would have left the box of rat poison sitting in plain sight and put the suicide note out on the table, and then sneaked out. A pretty good plan, and I would’ve believed it if it wasn’t for the letter the boy had just written to his mother.”

“The killer is very clever,” Sarah pointed out. “That’s twice he’s almost convinced you his victims killed themselves.”

Sarah got up and poured him some of the freshly boiled coffee. He’d finished the cake and was rubbing his chin thoughtfully.

“A killer who thinks he’s clever is usually pretty easy to catch,” he remarked. “You just have to figure out how to let him outsmart himself.”

“Are you suggesting we wait until he kills someone else and gives himself away?” she asked in alarm.

“Not exactly,” he said. “I was thinking more about letting him think he got away with Calvin’s murder. Nobody has to know just yet that it wasn’t a suicide.”

“But would you be able to continue with the investigation if everyone thought Calvin had killed his father?”

“I could pretend I didn’t find the suicide note,” he mused, obviously still working this out in his head.

“Then you could pretend you still didn’t believe Calvin was the killer, or at least that you’re not sure,” she suggested.

“That’s right. And only the killer would know about the note. He might give himself away if he thinks I didn’t find it or was trying to conceal it.”

“I suppose you’ll have to speak with each of the suspects, then,” she said.

“I’ll certainly have to notify them of Calvin’s death, just to see their reactions, if nothing else.”

“Potter will be relieved, even though he’s not the killer,” Sarah said. “I’m sure Mr. Symington will be, too. You’ll have to be careful with him, though. Men like Maurice Symington don’t appreciate being visited by the police, and if he thinks you’re considering him as a suspect, he can make your life very difficult.”

“I know,” he said with a frown. “I think I can get by with pretending I’m just notifying him personally in case there’s anything he wants to do to hush things up and prevent a scandal over the boy’s identity.”

“That’s a good idea. We already know he was aware of Blackwell’s previous marriage and had met Calvin. Don’t be surprised if he pretends he didn’st, though. He may decide that denying the whole thing is the best course of action.”

“I won’t be surprised at anything Symington does,” he assured her.

“At least now you can eliminate the Fitzgeralds as suspects, and all of Blackwell’s other clients, too.”

“And why is that?” he asked with amusement.

Sarah didn’t like it when he found her amusing. “Because they would have no reason to kill Calvin,” she pointed out quite logically.

“Unless it was to throw suspicion on him, which is the reason he was killed by whoever did it,” he pointed out right back. “Of course, they’d have to know about Calvin and his relationship to Blackwell. That’s not something Blackwell was likely to share with paying customers.”

“Wait, the Fitzgeralds knew,” Sarah remembered.

“You mean Blackwell told them?”

“No, remember they were talking to Calvin after the funeral. I heard Mrs. Fitzgerald asking him about his relationship with Blackwell. He looked very uncomfortable, so I told him you were looking for him, to give him an excuse to get away.”

“That’s right. You said they had his life story by the time you interrupted them.”

“I was exaggerating a little. Oh, dear, what did I hear them saying? Something about how much he resembled Blackwell, I think, so they must have discovered the relationship. But even if they did find out he was Blackwell’s son, why would they imagine Calvin would have a reason to kill his father unless they knew the whole story? Calvin didn’t have time to tell them, even if he’d been willing to confide in total strangers, which I doubt. And we’ve already decided Blackwell wouldn’t have told his patients.”

“Clients,” he corrected her absently. “The killer addressed the suicide note to his mother, too. Anyone finding out Calvin was Blackwell’s son would naturally assume Calvin’s mother was dead, since Blackwell had remarried, so whoever killed the boy had to have known the whole story. It doesn’t seem likely the Fitzgeralds did.”

“Unless-” Sarah began, stopping herself when she realized how silly this was.

“Unless what?”

“It’s a little farfetched,” she warned.

“Say it anyway.”

“Remember that Potter was going to meet with Mr. Fitzgerald the day after the funeral. What if he told Mr. Fitzgerald about Calvin?”

“Why would he?” he asked skeptically.

Sarah tried to reason the way Potter might have. She was amazed at how easy it was. “He’s mentioned several times that Blackwell trained him in his techniques. If he wants to set himself up in practice, he’ll need to win over Blackwell’s patients.”

“Clients,” he corrected her again, this time with a wry glint.

She ignored him, still thinking. “Maybe he was afraid they’d be too loyal to Blackwell, and he wanted to ruin the good doctor’s reputation so they’d turn to him.”

“That’s stupid. They’re just as likely to turn on Potter for speaking ill of the dead,” Malloy pointed out.

“Potter might not realize that. He doesn’t strike me as very bright about dealing with people.”

“He’s not,” Malloy agreed. “Of course, Fitzgerald would’ve had to have a reason to kill Blackwell in the first place.”

“We decided he was jealous because of Blackwell’s attentions to his wife,” Sarah reminded him.

“No, we didn’st,” Malloy contradicted her. “Besides, Fitzgerald doesn’t strike me as the jealous type. He seems more likely to be motivated by greed.”

“Then he didn’t like the fact that his wife was letting Blackwell live in her house for free.”

“Then he could’ve had him evicted.”

“Malloy, you’re ruining my perfectly good theory,” she complained, getting up to refill his coffee cup.

“Murder just seems pretty extreme if you’re only unhappy about somebody’s living arrangements,” he said.

“I guess you’re right,” she grudgingly admitted. “Who else do you think could have done it, then?”

“I’m still favoring the young lovers.”

“Then you have to prove they knew about Calvin and his family,” she reminded him.