Steam train at Harringay station Sat* 0900 & Sun 1020 and a Pullman bonus Fri 0805

*Probably. The Lindum Fayre on Sat 7 Dec about 0900 should have been hauled by 'Duchess of Sutherland'. A problem with the 'black box' data recorder (yes trains have those too) can't be fixed in time.
It is expected but not guaranteed that 'Union of South Africa' will be repaired in time after an axlebox caught fire and will substitute - it is booked to travel to London Friday afternoon, follow its progress here. Excursion details here, live times here. If possible an update will be posted if the steam locomotive does not run, but it could be decided Saturday morning...

Sun 8 Dec about 1020, details here, live times here. Engine is the new-build 'Tornado'. The train calls at Finsbury Park so Tornado should be accelerating and working hard through Harringay on its way to Lincoln.

A non-steam bonus - 'The Apprentice' two weeks ago used the handsome and luxurious Belmond British Pullman train to host the grafters' task.
Friday 5th at 0805 at Harringay station you can see it for real (less steam engine) as it heads to Lincoln for the day. It will use the curve off the Gospel Oak - Barking line alongside platform 2, northbound.

Lindum (old name), Lincoln, Lincoln - anyone would think it has a large and famous Christmas Market.