He continues to stay

Much to your continued annoyance he remains steadfast in his seat. His eyes glued to his phone, seemingly idly scrolling through some never ending newsfeed.
But actually, perhaps this is as fun as anything. Baylie seems to be enjoying herself and the more you think about the more you find yourself enjoying the idea.
Your start to increasingly test the waters, so to say, by homing in on her nipples and giving them both a firm pinch. This elicits a sharp intake of breath, not very loud but you heard it. You also feel her body tense on yours, but as you let go she quickly untenses and begins to rock her body on your lap. Slowly grinding her legging clad ass over your now more than swelled bulge. You continue to pinch and play roughly with her tits, her reactions soon becoming only slightly ragged breathing. Her body completely at ease as she increasingly picks up the pace on your lap.
This chance is too good to pass up you think to yourself. So without warning you send your right hand down from her tits, tracing over her toned stomach to push straight past her hem and onto her pants. You fumble for a moment but slip your hand also past these whilst your left one continues to roughly manhandle her tits. You would have teased her a bit more, but you imagine the whole situation is teasing enough.
As you suspected; the heat and wetness radiating from her is instantly obvious as you let your hand rest a second over her vagina. You push back her lips and begin to massage her clit with your thumb. This gets a small squeaky moan from her. This causes you to freeze immediately and glance across to Duncan. Of course the idiot hasn't noticed a thing and remains glued to his phone. You can't help but smirk at this and continue the task at hand. You increasingly get bolder with your movements and soon she's beginning to let moans slip from her mouth.
As this happens she is increasing her grinding on you, soon it becomes apparent she's actually pushing into your hand. Demanding more from you. You slowly let your fingers leave her lips and move towards her insides. Just as your about to truly 'test the waters', with her body pushing against your hand as much as it can, Duncan speaks:

"Hah, you should look at this tweet. I've just sent you it babe," he had said this looking up at both of you, or atleast your heads, but almost instantly his head goes back down. You both take a moment to unpause. You're shocked he didn't notice something. Baylie is clearly flustered, her cheeks red and breathing heavy. Whilst he was talking to her she was biting down heavily on her lips to control herself slightly. But after that, well he's truly oblivious.
So,you might as well continue full throttle. With that you send your fingers inside of her. Your thumb stays on her clit as you begin to finger her. It doesn't take you long to build up speed and intensity. Her moaning she's having to clearly stifle by basically chewing her lip off. Her hips thrusting into your hand as you move it about. Her top has also slid basically up to her tits due to your rough handling of them with your left hand.
Her moans must surely be audible to Duncan by now, but seemingly not. You can feel her body is beginning to get close to orgasm and she's fully coated your whole hand in her juices, even the fingers not sliding in and out of her warm body. She starts mumbling very softly about how close she is. You don't need much more encouragement and intensify your effort on her body. Slipping a third finger inside of her and increasingly having your fingers curl around inside of her body as your thumb rolls her clit around. Her body is beginning to quiver and shake slightly even as she continues to grind on your lap.

"Almost" she mumbles weakly to you, you can tell she's moments away now.
Suddenly out of nowhere once again Duncan speaks

"Hey, are you guys almost finished up yet?" he asks glancing up briefly. At this Baylie can't handle it and she begins to orgasm. You'd instinctly stopped at his voice but as her body begins to convulsed around your hand and on your lap you move your fingers slightly.
She's clearly struggling to contain her moan as she's biting her lip hard and making vague 'nghh' noises. After a few seconds of a clearly fairly heavy orgasm she begins to come back to it.

"Yes love, we're finishing up now it seems," she replies to him after atleast a 30 second delay.