Having WAY too much time on my hands...
What we know:
1) Somebody blew up Dulinor on his way to assassinate Strephon on 131-1116
2) Strephon was not on Capital at the time but off visiting Longbow and didn't arrive back till 212-1116 (71 days or 10 jumps after the assassination).
3) Between those two dates the following happened: several high ranking (and assumably in on the plot) officers in the Ilelish Guard Regiment are replaced, Norris and Isis are formally appointed to Archducal rank, Prince Varian decides to leave Capital.
What does this give us?
It looks very much like somebody other than Strephon organised all this and did so without Strephon's direct approval. The question is who? as its very likely the POD revolves around them. The individual would need to have Strephon's complete and utter trust and confidence.
And the Nominees are: (drum roll please)
a) Iolanthe
b) Iphegenia
c) Varian
d) Isis
e) Tranian
f) Norris
Tranian, while extremely well trusted by Strephon, lacks the "clout" to to pull a stunt like this without some serious repercussions even if right. Isis and Varian are not close enough to Strephon to even try it. And Norris is off in Deneb and again not close enough to Strephon.
This leaves Iolanthe and Iphegenia. Iphegenia is too young and again probably lacks enough of Strephon's trust. Leaving... Iolanthe.
So if we assume Iolanthe arranged "the hit" and subsequent events we need to figure why. Presumably somebody or something tipped her off. It would have to be somebody she trusted completely (even for Iolanthe, this is a huge stunt to gamble on). The candidates are the same five as above.
Norris is in Deneb, Isis is close to Iphegenia not Iolanthe, and again Varian isn't close to Iolanthe either. This leaves Tranian and Iphegenia. Iphegenia has the edge in trust, but Tranian is still in the running. Actually to convince Iolanthe to act would probably take more than either one on their own, so lets go with both Tranian and Iphegenia approached Iolanthe.
Soooo... who tipped them off? Isis may well have known her father's plans and sent warning to her close friend Iphegenia who then went to Tranian to get his support in going to Iolanthe. Certainly fits with her rapid confirmation. If there were any doubts at all she was in with Dulinor her confirmation would have had to wait till Strephon got home. She appears to be most likely.
Giving POD: Isis sends a waring to Iphegenia.
Of course personally, I still go with time travelling MT adventurers in a misjump
