This route is best travelled at low tide - at high tide it will be a long bush-bash to Overlander Stream.
Follow the shore west from George Sound Hut - crossing the generally small and well braided Katherine Stream. It is possible to remain on the shore for about 1.5km with a few brief climbs or wades round boulders. About 400m before Overlander Stream the shore becomes sheer. Make a steep ascent 60m or so up the gully before the bluffed section, ensuring that you are high enough to round the head of the following guts and bluffs, before following deer trails sidling down to meet the shore at the Overlander mouth.
Moirs describes a route round the shore for a further 600m to behind island '22' followed by a sidle below and through bluffs to gain the base of the spur climbing south. I could find no way of following this route that did not involve swimming. Instead I took Moir's advice that a '400m scramble' from 'the bay' will gain the ridgeline. Sadly the guide does not say which bay (Overlander, or the small one to its north) nor does it make mention the various layers of bluffs that must be negotiated on the way.
I climbed the face behind the small bay north of Overlander stream, winding my way generally south as I hit each ascending line of bluffs until progress south was blocked, at which point a seriously steep scramble through the last line of bluffs was required to reach gentler slopes above. I do not recommend this route, but can confirm that it is possible. Maybe the faces a bit up Overlander Stream would be easier?
Once on the ridgeline a series of steep, scrubby, untracked climbs and plateaus lead finally to pt564 - where good solid deer trails commence. From pt564 south travel up Overlander Spur is straight forward on good deer trails through first bush and later low scrub and rock slabs. Good view points exist in scrubby clearings around 1km before pt886. Good dry campspots exist here, if the various small water holes hold water - but note that they are reported to dry out.
500m before pt886 a creek drains east off the ridge, providing water and swampy going. Beyond, deer trails became fragmented and a few hundred meters of bush bashing was required to reach the 886m highpoint where more clearings awaited.
Drop briefly SE off pt886 until a dropoff is reached with bush below. Swing south along the escarpment and pick up the spur dropping first south then SSW as indicated on the map. Keep on the spur close to the steep dropoffs to the west, rather than dropping onto the confused eastern face. A creek forms to your left and you need to ensure you end up on its true left before it gorges deeply out and drops away to the valley to the west. Follow the spur on the true left of the small creek, dropping just east of south towards the basin below. There are small tarns where the spur hits flats (200m SE of pt575), and allegedly viable campspots.
From the tarns continue to drop just east of south into the head of a significant creek. This is NOT a continuation of Ethne Stream (but is indicated as such on current LINZ topomaps) as you'll find out as you drop. Continue to descend south, following either the very steep creekbed, or the very steep spur on its true right, sticking close to the creek. At about 400m the creek swings west and drops towards the South West Arm in a series of waterfalls. It is necessary to cross the creek to the true left bank just at the head of these falls - a sole surviving red permolat marker still marked this point (2019). After crossing the creek, sidle the face, dropping south and picking your way down through various strata of bluffs until you are NE of Ethne Saddle and maybe 40m above it, at which point you can swing SW down the spur to the saddle itself.
From Ethne Saddle drop SE into what is truly Ethne Stream - there are few deer trails and it may be slow going. Follow the initially boggy stream down until good deer trails climb the true left bank - follow these as they climb onto the terrace east of the stream and then follow it down to its confluence with the Stillwater.
There was formerly a walkwire over the Stillwater at the exit of the gorge at this point. Now, however, the best crossing is on a good shallow gravel bar downstream of the pool, 200-300m downstream of the falls.
Good dry campspots exist on the silt banks of the stillwater on either bank - you can find spots 4m above the river level, but having witnessed the river rise 2m after one day of rain - be aware that they may flood in extreme weather.
George Sound Hut to Overlabder Stream: 2km, 1.5-2.5 hrs
Overlander Stream to pt 886: 3km, 3-5 hrs
Pt 886 to Ethne Saddle: 2km, 2-4 hrs
Ethne Saddle to Stillwater-Ethne forks, 1km, 1-2 hrs