As Hammond is passing by, he should let him bring the towels.

Just as John was contemplating his options in front of the closed door, Hammond had the great courtesy to come into the common office area. "Jeez, what an incredibly fucked up weather!" He exclaimed while he dumped his wet pack on one of the tables. "I am soaked right down to my crack, after biking only 15 minutes from home!"
John nodded agreeing, still standing perplexed with Hammond his sudden entry.
"You also got wet, mate?" Hammond asked him, pointing at the towels in his hand. "I thought you came by car? Do not tell me you need two towels to dry yourself after those couple of meters from your car to the entrance?" John contemplated his options in a split second. Surely he could not go in right now as Hammond was looking at him straight on. There was a huge chance he would just follow him or would become suspicious if he would close the door completely. Looking through the small window thoroughly enough and you would be able to see the entire office. Again a mental picture arose of John needing to explain exactly why he was standing there in the office with a half-naked Sarah and he felt a sudden urge to run.
In any case he could not just stand there without making a choice, as the office might become even more crowded in time. That would surely complicate things for both Sarah and John.
With a rough voice he tried to explain the situation to Hammond. "In fact... Sarah is in there, half-naked..." Hammond his eyes were opened wider than he had ever seen as he heard John say he had an almost naked babe in his office. "She thought she could change her clothes in my office peacefully," John continued, "but she needs towels to dry herself." He made a gesture with the towels towards the door. "She just does not want to grab them by the door as she is afraid people might see her through the window, you know? And honestly, as a married guy I am a bit afraid to go in there. Imagine how it would have looked like if I was in there and you would have come in as you did?"
Hammond uttered a short, sharp laugh and straightened his stance as to say: 'I will save her for you!'
But then most likely in a more randy kind of way. Sure enough, his words backed this idea. "Do not worry, I am not married so I can get you out of this twist..." In a softer voice he continued, looking around to see no one else was there. "In fact, I have been dying to see her naked ever since she walked into this very room."
Confidently he grabbed the towels from John his hand and marched towards the door. John felt like he was kind of violating the trust Sarah had placed in him by chickening out of delivering the towel himself and nervously moved towards the exit. Just as he left, he looked around to see Hammond entering the office space and the shock on Sarah her face as it happened. He could not really hear them speak, but her face showed pure terror, then acceptation and, as he moved closer to her, a faint smile of temptation.

Again John felt a jab of jealousy and cursed himself for not being more of a true man, but then shrugged it off and decided he did need coffee after all. As the office door slammed shut he imagined to let it go completely, but one last look made him worried more than before. There she was, her almost naked body hugged by Hammond his strong arms as the towels had been dropped to the floor. She was none the wiser as she offered her male intruder a sly and enticing look, but John was all to much aware that the couple was plainly visible through the small window. As Hammond leaned in for a kiss, John felt obliged to watch. Out of curiosity for a form of peepshow or a misguided sense of being the protector of their decency he did not know for sure, however John felt it absolutely critical to make sure they were not spotted by any other co-worker. So to be able to fulfill that role in the best way possible, he found himself a slightly hidden spot where he could see both the door of his office, as well as anyone coming in to the common area unannounced. Within seconds he was hooked however, forgetting to watch the entrance completely as Hammond unclasped Sarah her bra and let it drop to the floor.
Even from a distance her breasts looked incredibly perky and responded directly to Hammond his hand that was clasping on the right side. He gave it two squeezes to get a feel of her firm chest and then proceeded to circle his index finger around her nipple, causing Sarah to tilt her head into the back of her neck in joy. Back went his hand to gather all of her breast in the palm, while her nipple pierced in between his fingers. He brought down his head to produce the same circles his fingers had just been, only this time with sensual movements of his tongue. Sarah seemed to enjoy that thoroughly by the look on her face as her hand slit under Hammond his blouse, down his side to his pants and slowly grazed across his slightly growing bulge. Indicating that she definitely wanted this to go on to more escalating activities.
Hammond proceeded to push up her left boob by placing the palm of his left hand under the breast and taking the nipple between his lips. At first he looked to be giving a sucking motion onto the sensitive extension, but soon went on to very gently putting the nipple in between his teeth with very low pressure. Sarah shrieked a bit, almost audible by John in the other room, but enjoyed it all fully.
To advance the play, Sarah now took action by pulling his arms to Hammond his sides and starting to unbutton his blouse from the top. Soon enough the shirt was pulled open and she proceeded to kiss his toned chest. Directly during these motions, her hands searched for his belt and the button of his trousers and before long also these touched the floor. Hammond was now standing there with a bare chest and from the waist down only in navy blue boxers, in which, as even John could see from a distance, he was sporting a really decent size erection.
He took the opportunity of the moment of peace as Sarah was observing him, to gain back control and to start his plan to bring her to a state of being ready to be taken. Before Sarah knew what was happening, he had grabbed her by her sides, pivoted her 180 degrees and placed her upper body down so that her perky boobs were resting on John his desk, slightly compressing them. As a result John made a mental notice to himself to warn the cleaning ladies that he would clean the desk by himself... Only to of course conveniently forget that one spot.
The ass of Sarah was now slightly raised above the rest of her almost horizontal body and he had easy access to pull down the light grey lacy panties from her hips. As these last undergarments touched the floor, so did Hammond. He got down onto one knee and proceeded to give some gentle kisses on the back side and inside of her legs, spreading her a bit more before heading for the money shot.
Unfortunately John was not sitting at the correct angle, and possibly too far away, to see what was happening directly. But from the height of where Hammond was pushing his lips and tongue and her reaction to it made it clear to him what his play was. At first he went in for the tease at the height of the most likely moist and welcoming lips of her vagina. No doubt he would run his tongue along side the edges of the outer lips, before slowly moving into the center to hover in the no-mans land between the clit and the hole itself, finishing with a slight poking of the tongue into the hole. 'At least,' John thought, 'if he was any good in it.' Like John considered himself to be.
Next, Hammond his face went a bit further down and was pushed a tad more in between the legs. Sarah her legs began to jerk a bit and her face was suddenly twitching, telling John that Hammond was most likely encircling her clit with his tongue. Varying pressure and sometimes even a gentle sucking between his lips, that would be the ideal motions here. Sarah was enjoying it more and more and the door and window at the entrance of his office were no longer sufficient in silencing her testimonies of ecstasy. Being the secretive on-looker of this erotic love fest and hearing his adoration moan this passionately, simply was too much for John. He untied his own pants and pulled out his cock, severely stiffened by the action unfolding in front of his eyes. Still somewhat nervous about his own public position in the office, he decided to wank it only slowly, partly covered by the desk he was sitting at.
In front of him Hammond completed his oral routine by giving her a firm teasing with the tongue at the level of her butt hole, sending further shivers down her spine. Thereafter he righted himself, standing next to her, before running a finger of his left hand outside her lips to get them wet. Apparently Sarah was dripping wet, because almost immediately he pushed the finger deep inside her, making her gasp with her head resting on the desk. As two, and then three fingers of the same hand were making their way inside her, his right hand pulled down the edge of his boxer short, allowing his erect penis to spring to freedom. Hungrily she looked back along her shoulder, while he placed some spit on his right hand to lubricate the tip of his cock with. Then he took the last few necessary steps towards her to rest the head of his pole on her leg and pulled out his fingers. As the tip rested now firmly between her vagina lips and against the hole, Sarah looked ever more impatient and seemed to almost wanting to jump back onto his cock immediately. Extremely slow the head disappeared from John his sight as Hammond pushed it inside her and kept going until his hips were touching her ass skin to skin. With every new inch of his manhood poking inside her, Sarah got into a higher state of arousal and soon her eyes were shut to enjoy the feeling to the max.
As Hammond picked up the pace, pounding inside her with long, decisive strokes, her moaning returned. John, now almost frenzied by the hardcore action showed, felt his own cock stiffening even a bit further, his tip now touching the cold underside of the desk.
They quickened the pace even more and John could swear he saw his heavy desk move by the pressure Hammond was putting in with each slap his hips made against her backside. Her breasts were, as pressed as they were against the surface, slightly moving back and forth over the smooth wooden desk.
Also picking up the pace with his hand on his own cock, John tried to imagine the warm feeling of Sarah her pussy all around his manhood and the top view of his boner sticking between her legs from Hammond his doggy-style position.
For a few minutes, Hammond kept pushing his stick in and out the slit of Sarah, until she pushed her upper body up, signaling him to back up for a bit. No doubt the guy was now feeling a throbbing sensation in his balls he just had to unleash, but he willingly agreed with Sarah, interested in what she would do now.
She again turned around those 180 degrees and placed her butt firmly on the desk.
'Another place that would never be washed again.' Vowed John as he could see from his angle the glistening moisture dripping from between her opened pussy lips as she raised her legs up and to the sides.
Hammond immediately guessed what she wanted and walked further up to the desk. Soon his cock was pushed back into her pussy and as his hands searched for support on the sides of her ass to ram it deeper home, her arms folded across his neck and her head landed on the top of his chest. Without delay Hammond picked up the pace he held earlier and Sarah her moans were heard even more pronounced through the office door. Her breast were flinging around; up and down and to the sides on the motion of his thrusting. As her legs loosely folded across his lower back and he held her ass tightly in the spur of the moment, John guessed they would not even need the desk in the first place. Hammond could have held her in mid-air, banging away into her slit.
All of his muscles were flexing as he was hammering away and the distinct sound of flesh slapping flesh not too softly could be heard through the wood and glass barrier in between them and the observer.
For a few minutes the scene continued; Hammond sweating and pounding, Sarah moaning fiercely and slightly convulsing on his cock, John just as fiercely jacking off under the desk.
All of the sudden, his ass cheeks pulled together and his nails seemed to want to bury themselves into the flesh of her backside as Hammond unleashed his sperm deep inside her pussy. His pace became irregular, signalling the end of the ride for Sarah. She seemed to manage well enough to hide the disappointment of an uncompleted orgasm run as she looked into Hammond his eyes as he pulled his limbering cock out of her vagina, giving her one more jolt.
A tad surprised John then saw that Hammond turned out to be a regular team player, as he immediately pulled Sarah closer to the edge of the desk, got down on one knee and started pleasuring her orally.
Again John was sitting at the wrong angle, especially since her leg was now placed squarely in the way on Hammond his shoulder. But since John was actually real close to coming himself, he did not really mind at that moment. As Hammond started apparently to focus his tactic directly on her clit that was already tingling from excitement from the fucking, Sarah dropped onto the desk with her back and placed her hands on his head.
The pure sight of Sarah leaning back naked and sweaty on his paperwork, with her breasts dancing up in the air in the motion of her labored breaths, moaning and biting her lips out of ecstasy caused by the tongue on her pussy, **** John to push his cock back into his pants and to head post-haste to the bathroom. There he dove into one of the stalls, pulled out his hard and throbbing member with a piece of toilet paper and finished the last few strokes envisioning that he was the one looking past her belly button and beautiful tits to her face, having his tongue in her slit. Needless to say he came swiftly and hard, filling the paper with powerful jets of cum.

The remainder of the day he did not see Sarah nor Hammond anywhere in the building and as he headed for home at the end of his work time he felt somehow incomplete. John had the urge to make sure they did not know that they all shared a moment, even though they had seemed to be unaware.
In the evening, as he was sitting next to his wife Celia on the couch watching TV, his phone bleeped about an incoming text message.