Horatio has a kind of power over math, over numbers. He has a fundamental understanding of them that will only serve as further aid as he climbs the ranks — it's a skill nothing short of impressive, sometimes even brilliant in the right circumstances.

William has no such gift. With Archie moving to join them, he finds himself a little unsure of their angles, of this shape it is they're supposed to be making. He feels Horatio's hand at his back like a ball of heat; he feels a similar heat from Archie, in his proximity alone. That's what he gives himself up to, in the end. That's what has him turning just enough to welcome Archie into their embrace, to go searching for the other man's fingers while the arm he has around Horatio curls a fraction tighter.