Sequence 9 - Double Trouble and Dress to Impress: Assassin's Creed: Syndicate Walkthrough
After Assassination of Maxwell Roth, Starrick had decided to take over the Shroud of Eden by himself and control London. The Frye Twins had decided to Enter the Ball event, but they need entry passes which Green will help them out with Sequence 9: Double Trouble and Dress to Impress.
Jacob and Evie decided to Enter Ball event in Buckingham Palace, but as Miss. Disraeli informed you can take away Gladstone's passes to enter. You must Locate them at their House first. Then Speak to the children nearby to know their Exact Location.
Now Reach the current Gladstone's location and steal his entry pass. Later locate Mrs. Gladstone and steal her pass as well. Note that you don't have to kill any policeman during this process(side objective).
Once you are done with stealing it's time to steal the Gladstone's carriage as well to Enter Buckingham Palace with pride. Another side objective not to damage Gladstone's carriage. Deliver Mrs. Gladstone's carriage to Mr. Abberline to end the mission.
Sequence 9 - Dress to Impress
You need to Enter Buckingham Palace unarmed, but Mr. Abberline can help you to take your arms inside. You must Locate the Royal guards in St. Martin Church and Knockdown one of them, steal the Royal uniform and hide his body in a carriage. Side objective is not to kill anyone.
Now return the Royal guards Clothes to Mr. Abberline so he can enter in the Ball in disguised. Here Ends the Mission and the second part of Sequence 9: Dress to Impress.