Modesty's background is an interesting mystery, both to others and to herself (here's O'Donnell's RL encounter that he later used as the basis for Modesty's own history) ... she's unsure of her actual name or age and so has arbitrarily chosen her own monicker and birthday, she's smart and pulled off an audacious plan to gain her own personal and financial independence by temporarily taking control of a crime syndicate, then retired from that to live an "honest" life once she met her goals. Sounds like a rather far stretch as I type this, but O'Donnell has made this whole backstory absolutely believable. Willie became her trusted and devoted lieutenant during her shady days and chose to also go straight at the same time as she did rather than work for anyone else. The pair aren't, never have been, and never will be lovers (they both find the notion hilarious and pursue separate love lives), but they have quite realistically become and remain the best of friends, with absolute respect for and trust in each other. He's "Willie love" to her and she's always "Princess" to him. The pair aren't perfect ... they each have their strengths and weaknesses and reasons they really need each other. And they've both learned that leading safe lives is far too boring if they don't spice things up with adventure once in a while. So being approached by Tarrant of the British Secret Service, who needs a little under-the-radar favour, is the beginning of something splendid ...
From the original novel, "Modesty Blaise":
Her tone sharpened. "What the hell got into you, Willie? We quit, didn't we? No more crime. We made our pile, split up the organisation, and quit."
"I wasn't going bent again, Princess--"
"Be quiet and listen, Willie love." She felt the swift relief in him at her use of the old familiar term. "You've got a bankful of money and a nice little pub on the river. All you ever wanted. So why come out here and get tangled up as a mercenary in a banana-state revolution?"
Willie sighed. "My manager runs the pub better'n I could," he said with a touch of bitterness. "I was going bonkers, Princess, honest. Up the wall. I 'ad to 'ave a break."
"Did you have to get caught? And my God, stay caught? Willie, it's humiliating. You've gone solo for me often enough before."
"Yes--for you. It's always been easy when you told me to go an' do it." He ran his hand through his hair. "I just couldn't get me 'eart into this lot, Princess. Being on me tod, everything just seemed to shut down. I was scared it might ... but I 'ad to do something." He inhaled broodingly on his cigarette. "It's no good. Retirement don't suit me some'ow. I dunno 'ow you stick it," he ended respectfully.
Modesty swung the car off the main road and on to another track, following Santos' careful instructions to the letter.
"Neither do I," she said in a neutral voice. "This is the first time I've come alive in a year."
Willie sat up straight and turned to stare at her.
"Well, then," he said softly. "Look, suppose we went back on the old caper, Princess? Start fresh and build up a new Network--?"
"It wouldn't have any point now. We've got all we wanted. And without a point, we'd soon lose out."
"Then what we going to do?" he asked helplessly. "I mean, just for a break now an' then! You know how it is, Princess. The bits between capers are good, but only because they're in between. Without the capers it's all just ... just stale beer."
"Tarrant's pay-off," she said slowly. "It's a job he wants done. But I don't know anything about it yet."
"Us working under Tarrant?" There was mingled hope and annoyance in Willie's voice.
"Not under. For him. On a particular job. And he didn't pressure me, Willie. But I don't know about "us". This latest effort of yours won't have impressed him."
"Ah, look Princess! That's different. You can tell Tarrant. I mean, I never laid an egg like this before, all the time I worked for you, did I?"
"No. But that's over now, Willie. I can't bring you in just because I might need help. It means you taking orders from me again. And you're a big boy now. I want you to be your own man."
"I don't." He spoke with flat desperation. "If you don't take me back, I'm a goner."
"Oh, Willie ... I don't know." She was troubled. "Look, we'll see what Tarrant brings. But I hate taking you for granted, and I won't have Tarrant do it, either. Just leave it with me and keep your nose clean. I don't want you in any more trouble."
"Don't worry, Princess. I've been a right burk. I'm sorry."
"I won't worry." The lights of the small border-post showed ahead, and she lifted her foot, turning to look full at him for a moment. Willie saw the rare smile that suddenly lit her face, the smile worth waiting a week for.
BTW, for fans of Charles Stross' "Laundry Files" books: the two "guest" characters in the latest (fourth) volume "The Apocalypse Codex" are tributes to Modesty and Willie ... there's a ton of inside jokes in that novel for those who've read O'Donnell's originals. ;-)
The novels (and a couple of volumes of short stories) in the Modesty Blaise series, in order, are:
A Taste for Death
The Impossible Virgin
Pieces of Modesty
The Silver Mistress
Last Day in Limbo
The Xanadu Talisman
The Night of Morningstar
Dead Man's Handle
Cobra Trap (do NOT read this last volume until you've read all the others; just ... trust me on this)
The Titan reprint volumes of the comic strip (so far), in order, are:
The Gabriel Set-up
The Black Pearl
The Green-eyed Monster
The Puppet Master
The Gallows Bird
The Inca Trail
The Lady Killers
The Scarlet Maiden
Death in Slow Motion
The Double Agent
Million Dollar Game
Lady in the Dark