In the last decade, Child and Adolescent Mental Health Services (CAMHS) have observed an unprecedented rise in young children presenting with suicidal ideation, needing urgent assessment and treatment. Once stabilised, CAMHS professionals often refer these children to speech and language therapists (SLTs) for assessment of and support for their social-emotional skills. The Secret Agent Society (SAS) is an evidence-based intervention for children with significant emotional regulation and social communication challenges. No published peer-reviewed evidence exists for the use of SAS for children with moderate-severe mental health disorders. This study aimed to evaluate the efficacy of SAS in an Irish outpatient CAMHS. Fifty-one children (30 boys, 21 girls) aged 8-12 years (mean age 10:11) with diagnoses of attention deficit hyperactivity disorder, anxiety disorder and/or autism attended the 14-week programme. Questionnaires were completed by children, their parents (51 mothers, 45 fathers) and teachers pre-intervention, post-intervention and at 3- and 6-month follow-up. Statistically significant improvements were made in children's social communication (F (1.985, 99.273) = 24.900, p < 0.001) and emotional regulation (F (1.787, 89.358) = 27.302, p < 0.001) across home and school settings. Children's knowledge of emotional regulation strategies also significantly improved. Treatment gains were maintained up to 6-months post-intervention. Results provide preliminary evidence for the efficacy of SAS in an Irish outpatient CAMHS. A cost--benefit analysis would determine the feasibility of offering SAS in other outpatient community services. SLTs have a vital role to play in delivering intensive social-emotional skills support for children with complex diagnostic profiles within CAMHS and other specialised multi-disciplinary teams.