"But I'm not happy," Di announced.  "I didn't get invited to the spring dance.  I even wrote to Miss Lonelyheart about it"

Mart gasped.  "Jeepers!" he exclaimed.  "So you did!  Consider yourself invited now.  By me!"

Brian grinned at Honey.  "How about it?" he said.  "Will you be my date on Friday night?"

Jim smiled as his sister nodded shyly.  "In that case, Dan," he said slowly, "that leaves only one female between the two of us."

Dan chuckled.  "But I'm already booked," he said.  "I'm taking Ruthie Kettner.  I guess you're going to have to take Trixie yourself."

Jim smiled and leaned toward her.  "What do you say, Trix?  Will you come to the school dance with me?"  His tone was light, but everyone could see that his eyes watched her closely.

Trixie's face flushed scarlet as she answered happily, "I'll be glad to go with you, Jim - unless another mystery comes along that I have to solve first."

The other Bob-Whites groaned in unison.

"Please - no more mysteries!" moaned Mart.

"At least, not until after the spring dance," added Jim.  He smiled at Trixie, and she smiled back, her eyes shining.  There would be more mysteries, she knew, but for now, the spring dance was enough to look forward to.

The Mystery of the Midnight Marauder (p. 210-211)

Title :
Trixie Belden and the Mystery of the Midnight Marauder

Author :
Kathryn Kenny
The ghost writer of this book is thought to be Joan Chase Bowden.

First Published :
1980

Chapter Titles :
1.  Odd Behavior
2.  Worries for Trixie
3.  Excitement at School
4.  Mart in Trouble
5.  More Worries
6.  Inside Crimper's 
7.  Mart's Confession
8.  Dreadful News
9.  The Letter
10. A Mysterious Figure
11. The Marauder Strikes Again
12. Reddy's Prison
13. A New Clue?
14. A Fresh Suspect
15. The Next Victim
16. Trixie Makes Plans
17. Caught at Crimper's
18. Marauder Is Revealed

Setting :
Sleepyside, New York

Synopsis :
Mart Belden is behaving mysteriously and when the school is broken into by a mysterious Midnight Marauder, he becomes the prime suspect.  Trixie and the Bob-Whites have their hands full solving the mystery of Mart's behavior, the disappearance of Reddy and Patch and uncovering the true identity of the Midnight Marauder before any more damage is done.

Characters : 
Trixie Belden
Jim Frayne - adopted son of the Wheeler's
Honey Wheeler - Trixie's best friend
Brian Belden - Trixie's eldest brother
Mart Belden - Trixie's "almost twin" brother
Diana Lynch - a Bob-White and neighbour
Dan Mangan - a Bob-White and Regan's nephew
Regan - the Wheeler's groom
Sergeant Wendell Molinson - head of the Sleepyside police
Mr Stratton - principal of Sleepyside High
Harrison - the Lynches butler
Lester Mundy - student and suspect
Ruthie Kettner - classmate and loner
Earl "Grandpa" Crimper - owner of Crimper's department store
Mrs Crimper - his wife
Young Mr Earl Crimper - his son and manager of the store
Vera Parker - reporter with the Sleepyside Sun
Margo Birch - New York antique dealer

Villains :
Margo Birch

Points of Interest:
It is March and Peter, Helen and Bobby have gone to Albany for a day to visit friends.  A string of incidents (storm and a wrenched back) keep them from appearing in this book except for over the phone.

Brian is seventeen years old still!  (p. 19)

The school newspaper is called the Campus Clarion and is six pages long (p. 39-40).  Mart later reveals that he writes the Miss Lonelyheart column.

Does Jim get the best lines or what?  "Come on, you guys!  Maybe the office is passing out free doughnuts or something."  (p. 43)

Did Trixie get hot thinking about Ben or Jim?  Maybe you can work it out:
'Once, during one of the Bob-White's early adventures, Trixie had pretended to like Ben a lot, even though everyone knew she liked Jim best.

Trixie could feel her face growing hot just thinking about it' (p. 47-48).

In the early books, Jim won't let anyone else train his pup, Patch except him and is determined to train Patch properly.  But it seems that he may not have succeeded:
'Patch, Jim's little black and white cocker spaniel, disciplined too late to be the hunting dog his master had wanted to be...' (p. 105)
Maybe it was all that time spent away on endless summer vacations?

Sergeant Molinson is christened Wendell in an article in the Sleepyside Sun (p. 153).