"Why?"

Jean revealed that twice she had seen Maud going into Nancy's room-yesterday, at the cottage, and then at the inn that morning.

"Really?" Nancy tried to appear nonchalant. "At what times?"

Jean was vague. She said that she had arrived at the inn shortly before lunch the previous day. "I was unpacking in my room," Jean went on. "I looked out the window and saw Mrs. Potter enter your cottage.

"This morning," she continued, "I was at the second-floor linen closet when I heard footsteps. I looked down the hall in time to see Mrs. Potter lock your door."

Nancy's mind raced. Was Maud directly implicated in the strange happenings at the inn? For what purpose had she entered the girls' rooms? It struck Nancy as odd, however, that Jean would inform on the woman who had helped her obtain a job. To the waitress she merely said, "Thank you for telling me."

"You and Miss Corning were lucky that you weren't hurt in the cottage fire," Jean remarked.

"Yes, very lucky," Nancy replied. Evidently Emily had said nothing to the servants about a bomb being the real cause of the blaze.

Nancy asked Jean if she had ever met a girl named Mary Mason from Dockville. "Mary used to work at the inn."

Jean wrinkled her brow. "No, although the name is familiar. Perhaps I once met a Miss Mason at one of the places I've worked."

They were now entering the business section of River Heights. Jean asked Nancy to let her off in the center of town. "I'm going to the optician's first. Then I'll go to my girl friend's."

Nancy stopped near Burk's Department Store. Jean thanked her profusely and got out. The young sleuth drove to a nearby tearoom for a quick snack. Then she continued on to Meadow-brook Lane, in an attractive residential section, where Mrs. Stonewell lived. Nancy soon spotted the number and stopped in front of an imposing Tudor-style home.

She hurried up to the front entrance and rang the doorbell. A maid answered. Nancy gave her name and asked to see Mrs. Stonewell. The caller was requested to take a seat in the living room.

A few minutes later Mrs. Stonewell, attractively dressed in a tailored sports suit, stepped into the room. With a gracious smile, she asked, "Is there something I can do for you, Miss Drew?"

"Yes, Mrs. Stonewell. I'm trying to trace a girl named Mary Mason," Nancy explained. "I understand she worked for you."

The woman's smile vanished. "Let's say I hired her. But I didn't get much work from Mary Mason. I discharged her after a month." She glanced at Nancy curiously. "You don't want to hire her?"

"Oh, no," Nancy replied. "She has some information I need. Do you know Mary's home address?"

"No. She lived in while working for me," said Mrs. Stonewell. "I do remember she occasionally visited a brother in Dockville. Whether or not she is living there, I can't say. Nor do I know the street address."

"One more question," Nancy said. "Did you ever miss anything while Mary was working for you?"

"Not that I know of."

Nancy thanked Mrs. Stonewell and departed. She decided that when she returned to Lilac Inn later that day she would go by way of Dockville. Her next stop was at Helen's house. Nancy rea.s.sured Mrs. Corning, who had read about the fire, of Helen's well-being.

"Nancy," Mrs. Corning said, "the newspaper didn't state how the fire started. I suppose the usual carelessness-someone tossing away a lighted match."

Nancy, inwardly relieved, replied that this was always a possibility. She did not mention the time bomb.

With additional clothes for Helen in her car, Nancy drove home. She found that Mr. Drew was out for the afternoon in connection with his case.

When Hannah heard Nancy's account of the fire, she exclaimed, "Even on a pleasure trip, Nancy, danger follows you!" She looked at the girl knowingly. "And what about this twin of yours? Has she followed you to Lilac Inn?"

"Hannah, you're becoming a detective," Nancy accused fondly. "Seriously," she added, "you guessed it. She even managed to fool a friend of Emily's fiance who's staying out there. But she vanished again."

Hannah sighed. "I'll certainly be glad when she's caught."

"I hope to do that soon," Nancy stated. "After I pack some clothes, I'm going sleuthing in Dockville." She explained about tracing Mary Mason.

"That's a terrible place," Hannah cried worriedly. "Oh, dear, I'd better go with you."

"Don't worry," said Nancy. "I'll be safe in the daylight. When Dad gets back, please tell him where I've gone."

Nancy quickly packed a suitcase. She also took along her spare set of skin-diving gear. Then, before leaving, she wrote her father a note telling the details of the jewelry theft.

When she reached Dockville later, Nancy glanced about in dismay. She was confronted with row upon row of dingy tenements. In which one did the suspect's brother live?

Nancy stopped her convertible and inquired of a stout woman where she could find a family by the name of Mason. The woman shook her head, evidently not understanding English.

"I'll try another block," Nancy decided, and turned into a winding narrow street which led along the river front.

She decided to inquire again and pulled up to the curb. She was about to alight when she glanced in the rear-view mirror. Directly behind her was a red panel truck. It looked exactly like the stolen vehicle which had forced her off the road. No one was in it, but the motor was running. Nancy turned her head to get a better look at the truck.

At the same moment she saw a large rock hurtling through the air toward her open window!

CHAPTER XII.

A Daring Plan BANG! The rock struck the door of Nancy's convertible, just as she ducked down. When Nancy cautiously raised her head a few seconds later, she looked all around to see if she could spot the rock thrower. No one was in sight.

Nancy glanced into the rear-view mirror again. The red truck had disappeared! Had the truck driver thrown the rock? If it had struck her, she would have been badly injured. A peculiar coincidence, at the least, Nancy thought.

Quickly Nancy climbed out and examined her car door. The rock had made a dent, but there was no further damage. She determined to continue her search for Mary Mason, and hailed a grocer's delivery truck which was coming down the street. When she asked the driver if he had seen the red truck, the man said No.

"Do you know where I might find someone here by the name of Mason?" Nancy inquired.

"Yes. Bud Mason. He lives in the next block, on Sixth Street," the man replied. "I've made deliveries there. It's number 12."

Nancy thanked him. She drove along the river, and turned left on Sixth Street. The houses here were in better condition than the others she had seen in Dockville. Number twelve was a white cottage with flowers bordering the front path.

When Nancy rang the bell, the door was opened by a red-haired woman of about thirty-five. She had clear-cut features and wore heavy make-up. She wore a snug-fitting lavender dress.

Nancy introduced herself and said she was looking for a Miss Mary Mason who had worked at Lilac Inn.

"You've come to the right address," the woman replied. "I'm Mary. Come in."

"Thank you." Nancy entered a room furnished with comfortable leather furniture, books, and several pictures of nautical scenes.

The woman eyed her caller curiously. She invited Nancy to sit down and asked, "What brings you here?"

Nancy explained that she was a friend of Emily Willoughby and was visiting at Lilac Inn.

"Miss Willoughby tells me you left because the inn was haunted," Nancy went on. "Since then, she's been wondering what you meant. I said I'd try to find you and ask."

Mary had listened attentively. Now she gave a high-pitched giggle. "So Miss Willoughby's getting scared. It's true-Lilac Inn is haunted!"

Mary proceeded to give Nancy a dramatic story of hearing footsteps at night when no one was around. She said that several times when she had been working late in the kitchen, a ghostly face had looked in the window.

"It's a spooky old place!" Mary shuddered. "I don't know how I stood it-the grounds are so lonely and creepy at night. Besides, commuting to my brother's here was too long a trip."

Nancy wondered if she were on the wrong track, after all. Perhaps Mary had left because of fright, and had wanted merely to find work closer to town.

The young sleuth looked around. "This is a pleasant home," she said. "Have you always lived with your brother?"

Mary answered readily, "No, just since I returned to Dockville, two months ago. I worked down South during the winter, and before that, out West. I hadn't seen Bud for a couple of years. When I came back here, he suggested I get a job nearby."

She paused. "Say, Miss Drew, how did you know I was in Dockville?"

Nancy explained about her call on Mrs. Stonewell.

Mary scowled. "That fuss-budget wanted a slave, not a maid. I was glad when she fired me."

Mary went on to say that after she left Lilac Inn, she had stayed here. "I'm keeping house for Bud until I find a really good deal."

"Oh-by the way," Nancy said casually, "the other day I found a note to the gardeners. I understand you printed it."

For a fraction of a second Nancy was sure she detected a startled look on Mary's face. Then the former waitress laughed heartily. "Oh, Miss Drew, isn't that funny you should have found that?"

"Then you knew lilacs are called 'blue pipes'?" Nancy asked. "And what in the world did the message mean?"

After a short pause, Mary answered, "I don't know. Someone asked me to write it."

"Who?"

"I don't remember his name. I wasn't there long, you know."

Nancy went through the list of names of the gardeners, but Mary still insisted she did not remember who had asked her to print the message.

"Another thing," said Nancy. "I phoned this house the other day and was told no Mary Mason who had worked at Lilac Inn was here."

Mary Mason flushed. "I don't know who answered the phone. Around here n.o.body calls me Mary. That's my business name. I'm Dotty Mae. My full name is Dorothy Mary."

"I see," said Nancy. "Sorry."

Mary stood up. "Hate to rush you, Miss Drew. But I'm er-expecting company."

She accompanied Nancy to the door. The young sleuth said good-by and went to her car. She started the engine, glancing surrept.i.tiously at the Masons' cottage. Nancy plainly saw the window curtain move, as if someone were standing behind it, watching her.

As she drove away, Nancy reviewed the conversation. Mary Mason had seemed quite friendly, and sometimes a bit flighty. Nancy reflected that Mary's explanation of the "blue pipes" note sounded logical, but that the woman's whole story had been overly glib. She had, Nancy felt, not been entirely truthful.

"Why didn't she want to tell me who asked her to write the note about 'blue pipes'?" Nancy's hands gripped the wheel hard as a startling idea occurred to her. "She's shielding someone."

"Blue pipes" was being used as a signal-perhaps between persons at Lilac Inn and an outside accomplice. Were Mary Mason and a gardener two of them? And could Maud possibly be a third member of the group? Were they responsible for the diamond theft?

"They're all familiar with the place," Nancy reasoned, "and might have learned of the secret closet."

If this were the case, she speculated, the three might have other a.s.sistants. "For instance," Nancy thought, "the woman who b.u.mped into me in Benton, whoever put the diamond in my purse, and the person who placed the bomb in our cottage."

Nancy felt excitedly that her theory was worth following. She decided to return home and see if her father were there.

When Nancy arrived she was delighted to find Carson Drew at the desk in his study. The lawyer went over the whole case with his daughter, then shook his head in amazement. "This is a many-sided case you've tackled," he remarked. "I'm inclined to agree that the mysteries at Lilac Inn and your impersonator are linked together, and that 'blue pipes' is a signal of some kind."

Mr. Drew leaned forward in his chair. "Of course," he said, "Emily should report her entire story to the police. If Maud Potter does hold a threat over Mrs. Willoughby, she'll be dealt with by the law.

"Frankly I'm more alarmed about the spear throwing and time bomb than any other angle to the case, Nancy," Mr. Drew said somberly. "You and Helen are in constant danger."

Nancy said she realized this. "I'll be on my guard every minute," she promised. "And keep my eyes and ears open for any more 'blue pipe' messages."

The young detective went across the room to hug her father. "Dad, it's so helpful to talk everything over with you."

Mr. Drew looked at his daughter keenly. "There's something else on your mind. Want to tell me?"

He had observed a troubled expression come over Nancy's pretty features. Now she replied, "Yes. Dad, what's your impression of Sergeant John McBride?"

"I think he's a fine, intelligent young man," Mr. Drew said. "And seems to be quite taken with you," he teased.

Nancy's face remained serious. "I like him, too. But-well, Helen has a feeling he's at the inn for some other purpose than just helping Em and d.i.c.k."

Mr. Drew shook his head. "Nancy, don't worry. John may have his own reasons for being at Lilac Inn. But I firmly believe he's not mixed up in any jewel theft!"

With a smile Nancy said, "You're such a good judge of character. I knew you'd relieve my mind."

The lawyer then advised his daughter, despite Emily Willoughby's concern, to phone Chief McGinnis and tell him the whole story.

"He can use his own judgment on how to proceed. Also, he can dismiss the police guard at our home."

Nancy put in the call and gave the chief a detailed report, including the appearance of the stolen red truck in Dockville.

"I'll notify the authorities there at once," he said.

She inquired if there were police records of Dorothy Mary (Dotty Mae) Mason, Maud Potter, or any of the gardeners at Lilac Inn.

"I'll check." When the officer returned to the phone, he said, "No, Nancy. Nothing."

She promised to keep in touch and hung up. The girl's thoughts spun from subject to subject. Suddenly a daring plan popped into her head. "I'll try it!" Nancy decided.

Again she picked up the telephone. This time she dialed Lilac Inn. Emily answered.