Xendengalis: Calls out "Please everyone, stay back and we'll lead them to you!" and falls back to the intersection (move only, so no AOO) to M16 (alexi is now in square O15)
Kerith: Also retreats back to the intersection. The best spot available is O16.
Blackwing: Guarding the east passage. There is a staircase back here, Mistress.
Huge Monstrous Centipede: Scuttles up to attack Norynth again, but he yanks his leg out of the way at the last moment and avoids its pincers.
Gertrude: (Has not been given a command to retreat, but I'm not a cruel DM. Usually.) Understands that the group seems to be running away and falls back and joins Xengendalis in M16.
Norynth: You make a tremendous attack with your bastard sword, two handed, but succeed only in adding a fresh gouge to the stones of the floor. (I will assume, at this point, that you would use this round's movement to fall back, rather than stay up front all alone. Feel free to correct me in this). You fall back and join Titus in square N16, drawing an AOO (misses) from the Huge 'pede in the process.
Alexi: still readying.
Michelle: Another magic missile goes streaking toward the huge monster, blowing a chunk out of its side. It doesn't look like it's in very good shape, but still is mindlessly going after the party.
Medium Monstrous Centipedes: Swarm forward and around the Huge centipede, blocking it off from the melee, and more or less filling the entire hallway between your new position and the Big Bug.
c1: draws an attack of opportunity from Oren as it scuttles to M15, but he misses badly. Attacks Xengendalis, apparently drawn by the scent of blood, hitting him for negligable damage. Xengendalis fights off the poison.
c2: moves to M14 and attacks Oren, hitting him for negligable damage and injecting poison, but he manages to resist it - for now.
c3: moves to N15, attacking Titus and hitting him for minor damage. Titus yelps. That stings!
c4: moves to N14 and takes a bite at Alexi, but manages to miss the wizard.
c5-c9: fill up the rest of the hallway between yourselves and the big 'pede.
Oren: You stab at c1, but your blade bounces off the hard shell.
Alexi (initiative changed to whatever number is right after the centipedes): Smiling at your perfect layout of opponents, you begin to cast Burning Hands, drawing 2 AOOs in the process. c3 misses, but c4 hits. CRITICAL! You take severe damage and struggle to maintain concentration on the spell. Alas, it is not to be, and you feel the spell slipping from your mind, while nothing emerges from your fingertips but a faint trail of smoke.
Titus: attacks c3, crunching its head open. c3 is dead.
Foran: (Sorry, I forgot to have you start playing last round. Let's assume you did). Your Inspire Courage kicks in, neatly canceling out the effects of Xengendalis' Bless spell with its more potent magic. Since you cannot reach an opponent even if you wanted to, you just keep playing.