John Godber's new adaptation of Jules Verne's 20,000 Leagues under the Sea suffers from a severe case of nearliness. It's not difficult to see the concept behind the script and the production, and certainly there's enough talent to make it work, but somehow it seldom comes off.

Early signs are promising. Pip Leckenby's set – false proscenium arch, winding staircase to the depths, surfaces decorated with elegant ocean maps – looks good. There is an effective framing device, Professor Aronnax's lecture to a learned Paris scientific society, and the dialogue and direction of the early scenes suggests the same element of semi-serious play-acting as the set.

Sadly, this balance is not preserved. Play and production seem unsure whether or not this is a parody and the hints of magic in the designs are not followed through. Mighty ice-floes, even the giant squid, go for little and many of the most dramatic parts rely on mist, smoke, rather a lot of shouting, crashing organ chords and Professor Aronnax's narration, well delivered by Joshua Richards. The balance of tone is lost in long passages of bombast and there are some bizarre elements, with Kim Hardy's performance as Captain Farragut and Captain Nemo's fish-like servant especially strange.

I don't know enough of the original to tell how far the disjoined narrative is present in Verne's tale. When the frigate Abraham Lincoln collides with the Nautilus, Aronnax, his assistant Conseil and the great harpooner Ned Land find themselves aboard Captain Nemo's submarine. Then follows a series of episodes: they eat the food of the seas, they explore the sea-bed and Ned rescues Nemo from a shark, they become restive and plan to escape, they are trapped at the South Pole, etc. The most important change to the original is turning Conseil into a woman, in disguise, devoted to the Professor. Though the excellent Heather Peace often convinces, it is an odd conceit, leading mainly to a couple of unmemorable heart-on-sleeve songs for the "invisible woman".

The cast of six deserves considerable credit. William Ilkley plays Captain Nemo with more than a whiff of both Napoleon and Peter Lorre; he musters plenty of impact, but no Plan B as the part becomes increasingly monochrome. Jack Brady as Ned Land is splendidly droll in early scenes with Aronnax and Conseil, but later has rather too much roaring to do. Joshua Richards' rumpled and passionate Aronnax is the nearest to a three-dimensional character and Sue Appleby compensates for her thankless role as society chairwoman with sterling work as keyboardist/MD.

Composer Stuart Briner's incidental music makes its effect and he produces one striking song, a jaunty music hall turn, "What about Me?", very well sung by Heather Peace in the role of a dead woman on the sea-bed! In fact the singing generally is very good. In a play which takes John Godber, much to his credit, out of his comfort zone, there is much to admire, but ultimately very little impact.

- Ron Simpson