Even if you don’t care for anything he’s done, you have to admire the way Robert Plant does it. Rather than pack out enormodomes singing about hedgerows, he detoured off into the trees altogether and, in the process, left all his contemporaries in the dust. We don’t even need to talk about his seventies band because, since returning to solo work with 2002’s Dreamland, he’s gathered musicians around him under various monikers – Strange Sensation, The Band Of Joy, The Sensational Space Shifters, and, not least, his deservedly award winning turns with Alison Krauss – that have allowed to him to drift wherever the winds may take him on a musical sea of his own devising.

The latest in this line are Saving Grace. This is their second Irish visit – they were simply astonishing in The Helix on the last one – for a tour that’s stopped in Cork, Galway and Sligo before getting to the Olympia and goes on to finish in Wexford. There are rumours – unconfirmed, so far – that an album is on the way. If they manage to capture even an eighth of the magic on display tonight, we’ll be talking about a very special record indeed.

Plant’s devotion to the blues is well-documented but the travels he’s undertaken as a sort of musical seeker in the last few decades have given him the means to combine African music, English folk, Appalachian blue grass, West Coast Pop, and anything else that took his fancy into a new blues, world music in the truest sense.

The stage is relatively simple. There’s a picture of a buffalo for a back drop behind three raisers; one for the drums, and two housing more stringed instruments than Grafton Street at Christmas. In front of that are two microphone stands and what looks like a well-loved rug. A violin and what might be a cuatro play as Oli Jefferson takes his seat behind the drums and Tony Kelsey and Matt Worley climb into their command modules. Plant walks on from one side and Suzi Dian from the other. ‘Gospel Plow’ goes back to the first Bob Dylan album and then much further back than that, an African American spiritual based on Luke 9:62. Jefferson plays a shuffle punctuated by the odd hit of bass drum and tambourine while Plant and Dian’s voice meld together, encouraging all to keep their hands on the plough, before they float higher again for the final plea.

‘The Cuckoo’ was recorded by Ramblin’ Jack Elliot but it also stretches back into history with variations of the song turning up in the Bodleian Ballad Collection at the end of the 18th century and there’s even an Irish song called ‘Bunclody’ that starts off praising the Wexford town before bringing the bird in question in for a later verse. Worley’s banjo takes it somewhere else again, making connections from Appalachia to Africa, while Kelsey’s mandolin floats about it, almost like a dulcimer, matching the rhythm of Jefferson’s bass drum.

‘Let The Four Winds Blow’ originally comes from Plant’s 2005 album with Strange Sensation, Mighty ReArranger. Dian adds bass in tandem with Jefferson ride cymbal, allowing the twang brothers to go to work on acoustic and baritone electric guitars. Plant, as he does throughout, steps back out of the way, allowing his bandmates to shine. “These are from Cuba,” says Plant, referring to the maracas he and Dian pick up when the song finishes. “An interesting place.” Worley takes the lead vocal on a great version of Leon Russell’s ‘Out In The Woods’ from his 1972 Carney album, with the three voices joining together then it’s Dian’s turn, Plant again standing aside to listen as she makes Sarah Siskind’s ‘Too Far From You’ her own. Worley bases a delicate solo around one teased and bent note with Kelsey’s tremolo guitar colours the air around him and Plant, when he’s not adding gentle backing vocals, stands between these two men, anxious to absorb what they’re giving out.

As if to prove, and not that they haven’t already, Plant’s assertion that this collective visit “all the different corners of the musical spectrum, we go back to the 1920s for Blind Willie Johnson’s ‘Satan, Your Kingdom Must Come Down’ and then Low’s ‘Monkey’. Plant previously covered both songs on 2010’s marvellous Band Of Joy record and tonight the former is built around a slide guitar as lonesome as the last man before the drums kick it towards a brief excerpt from ‘In My Time Of Dying’, another Johnson song, albeit one released under his name in 1926 as ‘Jesus Make Up My Dying Bed’. It’s as close as Plant comes to his former incarnation tonight, and his eyebrows rise when it wins a cheer. The latter selection makes connections backwards through this Minnesotan slowcore by way of the rumble of the toms and Worley’s lap Steel.

Plant jokes about going to America a lot as a young man, which he knows because he’s read about it. He thought he had a good grasp of what music was but when he decamped to Nashville around 2005, he discovered they had keys to music that he knew nothing about. He had been under the impression that Howling Wolf had the lot but then he heard the singing of Ralph Stanley and his brother Carter. Plant actually got to sing with Stanley on a version of ‘Two Coats’ on the 2015 duets album Man Of Constant Sorrow credited to Ralph Stanley & Friends, a song that Stanley first recorded with The Clinch Mountain Boys in 1971. It might not have been written about Plant but in “taking off the old coat and putting on the new” Plant found his second voice and whatever about squeezed lemons and Tolkienisms, this is the music he would seem to have been born to sing. There’s a mid-song guitar duet of guitar and banjo and then Dian’s accordion leads us down a French side street.

“What a difference it’ll make to your listening pleasure to tune into Ralph, but let’s go back to Duluth.” Another selection from Low’s 2005 album The Great Destroyer, ‘Everybody’s Song’ incorporates drum-led tempo changes for the chorus and Malian melodies from the cuatro. “There was other music I didn’t hear when I was listening to ‘Twists And Shout’. Moby Grape came and touched me on the shoulder,” Plant remembers by way of an introduction to a mesmerising reading of ‘It’s A Beautiful Day Today’ from their third album, Moby Grape ’69, with Dian stepping back a beat to echo the last chorus. ‘As I Roved Out’ stretches back further than memory - Planxty included a version on 1973’s The Well Below The Valley – but Plant acknowledges Sam Amidon’s take on it from 2013. Jefferson, Worley, and Kelsey are superb, unafraid, as all the best musicians are, to use space as another colouring in their arrangements.

“A lot of these songs potentially came from here. Appalachia and Mississippi have the same songs, just different ways of telling a story.” Plant first heard the next one from Donovan as ‘Hey Gyp (Dig The Slowness)’ but it’s really more Memphis Minnie and Kansas Joe McCoy. “We’ll pretend we wrote it. Don’t clap. It’s a court case,” Plant smiles before a blues promising to buy his baby a Cadillac. Richard Thompson is a “serious writer, a remarkable musician, and a great spirit.” Tonight’s version of 'House Of Cards' is slightly different from the one Plant recorded with Band Of Joy, with a guitar that sounds like it should be out on some great plain somewhere. After the band has been introduced, Dian leads us into a seriously groovy go at Donovan’s ‘Season Of The Witch’. As she calls on the band to stay in the pocket, where they would seem to permanently reside anyway, Plant veers into Buffalo Springfield’s ‘For What It’s Worth’. She responds with a line from Lou Reed’s ‘Walk On The Wild Side’, prompting him to have a playful go at ‘Black Dog’ before thinking better off it with a “been there, done that.” Dian offers ‘Aretha’s ‘Chain Of Fools’ which draws an appreciative glance from her elder. There’s more Stephen Stills before they tie it up, picking up every stitch to end this highlight of the evening, if it were possible to pick such a thing.

They finish the main set with a surprising ‘Down To The Sea’ from Plant’s patchy 1993 album Faith Of Nations and are rewarded with a standing ovation. They couldn’t possibly stay off stage for long and return with Los Lobos’ ‘Angel Dance’. Dian sashays across the stage as Plant displays the remarkable strength that his voice has retained. He’s not screaming like in the old days, he’s singing. All five musicians gather around a single microphone to send us out the door with ‘And We Bid You Goodnight’, another song that harks back past The Grateful Dead and The Incredible String Band to the time before electricity and amplification.

This encore sums it up. Plant is first and foremost a music fan, collecting songs from crossroads in Mississippi, villages in ancient Avalon and Hibernia, the mountains of Appalachia, camps in the Sahara, or los barrios de Los Ángeles, and adding them all to the pot. Saving Grace have the ears and the chops to go with him, wherever he pleases, although they lead him as much as he leads them. The rest of us were blessed to be in the room.