After they had reached the "Dick and Mary" stage she came right out one night and asked him.
"Hon," he told her, "that's one thing that I've got to keep from you for a while. It's nothing that you would be ashamed of, though, but something that will make you mighty proud. At least," he added, "It'll make you proud if I don't fall down on the job almighty hard. Meanwhile, all I can do is to ask you to trust me. Will you?"
The tips of her fingers rested on the back of his hand for just a moment before she said, "You know I will, Dick" – and neither of them mentioned the subject from that time on.
On the night of the Black Tom explosion, early in August, Dick didn't show up at the Library at the usual hour, and, while this didn't worry Mary, because it had happened several times before, she began to be annoyed when three nights passed the same way. Of course, she had no way of knowing that the Service had received a tip from a stool pigeon on the pay roll of the New York police force that "a bunch of Germans were planning a big explosion of some kind" just a few hours before the earth rocked with the force of the blow-up in Jersey. Every government operative in the city had been informed of the rumor, but few of them had taken it seriously and not one had any reason to expect that the plot would culminate so close to New York. But the echo of the first blast had hardly died away before there were a dozen agents on the spot, weaving a network around the entire district. All they got for their pains, however, was a few suspects who very evidently didn't know a thing.
So it was a very tired and disgusted Dick who entered the Library four nights later and almost shambled up to Mary's desk.
"I'll be off duty in half an hour," she told him. "From the way you look, you need a little comforting."
"I do that," he admitted. "Don't make me wait any longer than you have to," and he amused himself by glancing over the late seekers after knowledge.
When they had finally seated themselves in a cozy corner of a little restaurant in the upper Forties, Dick threw caution to the winds and told Mary all about his troubles.
"I haven't the least business to do it," he confessed, "and if the chief found it out I'd be bounced so fast that it would make my head swim. But, in the first place, I want you to marry me, and I know you wouldn't think of doing that unless you knew something more about me."
There was just the flicker of a smile around Mary's mouth as she said, almost perfunctorily, "No, of course not!" But her intuition told her that this wasn't the time to joke, and, before Walters could go on, she added, "I know you well enough, Dick, not to worry about that end of it."
So Walters told her everything from the beginning – and it didn't take more than five minutes at that. Outside of the fact that his people lived in Des Moines, that he had been in the Secret Service for eight years, and that he hadn't been able to do a thing toward the apprehension of a certain German spy that the government was extremely anxious to locate, there was pitifully little to tell.
"The whole thing," he concluded, "came to a head the other night – the night I didn't show up. We knew that something was going to break, somewhere, but we couldn't discover where until it was too late to prevent the explosion across the river. Now that they've gotten away with that, they'll probably lay their lines for something even bigger."
"Well, now that I've told you, what d'you think?"
"You mean you'd like to marry me?" Mary asked with a smile.
"I don't know how to put it any plainer," Dick admitted – and what followed caused the waiter to wheel around and suddenly commence dusting off a table that already was bright enough to see your face in.
"There wasn't the slightest clue left after the Black Tom affair?" Mary asked, as she straightened her hat.
"Not one. We did find two of the bombs that hadn't exploded – devilishly clever arrangements, with a new combination of chemicals. Something was evidently wrong with the mixture, though, for they wouldn't go off, even when our experts started to play with them. The man who made them evidently wasn't quite sure of his ground. But there wasn't a thing about the bombs themselves that would provide any indication of where they came from."
"The man who made them must have had a pretty thorough knowledge of chemistry," Mary mused.
"Mighty near perfect," admitted Walters. "At least six exploded on time, and, from what I understand, they were loaded to the muzzle with a mixture that no one but an expert would dare handle."
"And," continued Mary, with just a hint of excitement in her voice, "the bomb-maker would continue to investigate the subject. He would want to get the latest information, the most recent books, the – "
"What are you driving at?" Walters interrupted.
"Just this," and Mary leaned across the table so that there was no possibility of being overheard. "We girls have a good deal of time on our hands, so we get into the habit of making conjectures and forming theories about the 'regulars' – the people who come into the Library often enough for us to know them by sight.
"Up to a month ago there was a man who dropped into the reference room nearly every day to consult books from Shelf Forty-five. Naturally he came up to my desk, and, as he usually arrived during the slack periods, I had plenty of time to study him. Maybe it was because I had been reading Lombroso, or possibly it's because I am just naturally observant, but I noticed that, in addition to each of his ears being practically lobeless, one of them was quite pointed at the top – almost like a fox's.
"For a week he didn't show up, and then one day another man came in and asked for a book from Shelf Forty-five. Just as he turned away I had a shock. Apparently he wasn't in the least like the other man in anything save height – but neither of his ears had any lobes to speak of and the top of them was pointed! When he returned the book I looked him over pretty thoroughly and came to the conclusion that, in spite of the fact that his general appearance differed entirely from the other man's, they were really one and the same!"
"But what," grumbled Walters, "has that to do with the Black Tom explosion?"
"The last time this man came to the Library," said Mary, "was two days before the night you failed to arrive – two days before the explosion. And – Do you know what books are kept on Shelf Forty-five?"
"No. What?"
"The latest works on the chemistry of explosives!"
Walters sat up with a jerk that threatened to overthrow the table.
"Mary," he said, in a whisper, "I've a hunch that you've succeeded where all the rest of us fell down! The disguises and the constant reference to books on explosives are certainly worth looking into. What name did this man give?"
"Names," she corrected. "I don't recall what they were or the addresses, either. But it would be easy to find them on the cards. We don't have very many calls for books from Shelf Forty-five."
"It doesn't matter, though," and Walters slipped back into his disconsolate mood. "He wouldn't leave a lead as open as that, of course."
"No, certainly not," agreed Mary. "But the last time he was there he asked for Professor Stevens's new book. It hadn't come in then, but I told him we expected it shortly. So, unless you men have scared him off, he'll be back in a day or two – possibly in a new disguise. Why don't you see the librarian, get a place as attendant in the reference room, and I'll tip you off the instant I spot that pointed ear. That's one thing he can't hide!"
The next morning there was a new employee in the reference room. No one knew where he came from and no one – save the librarian and Mary McNilless – knew what he was there for, because his principal occupation appeared to be lounging around inconspicuously in the neighborhood of the information desk. There he stayed for three days, wondering whether this clue, like all the rest, would dissolve into thin air.
About five o'clock on the afternoon of the third day a man strolled up to Mary's desk and asked if Professor Stevens's book had come in yet. It was reposing at that moment on Shelf Forty-five, as Mary well knew, but she said she'd see, and left the room, carefully arranging her hair at the back of her